You would likely die from a Sta botch.
Depends how many botch dice you were using. Also, when you use it to keep yourself in the body you're currently in (just renewing the duration) you're not going to need the stamina check at all.
Botching the ritual itself is the more worrisome possibility. You'd want to master it thoroughly to minimise the chances.
Unless you've got a stamina of 3+, you'll die on a bad roll that isn't a botch. That puts the odds at death for the average target at about 1 in 5 per casting, and only supreme examples of human stamina are going to have better odds.
Also, creating a fresh living human is not easy - isn't it around base 70? Creating corpses is easy, but body-swapping into a corpse has a lot of very obvious problems.
I suspect anyone trying this approach is unlikely to last a decade.
As mentioned before; with the stamina check removed the year-duration version becomes a flexible spell. With the duration extended to permanent and the spell tweaked to 'mostly non-hermetic' it becomes a legitimate life-preservation necromatic-type spell. But with both the year duration and the stamina check it just feels too much hassle for what it does - and I think a magus would have to be legitimately insane to even consider casting it. Simply being amoral, sociopathic and self-serving doesn't preclude a person from being able to spot a dud. 
Anyway, been talking to the SG and there's definite agreement that the spell as-written is a flop. We might end up house-ruling it to something else - but I'm still interested to know if anyone else has actually managed to make the spell work in a 5th edition campaign. I'm talking someone actually legitimately casting it in a saga while being aware of the risks, etc. rather than just theory.
It doesn't even need to be "mostly non-hermetic" to be permanent. Give it a ridiculously high baseline, and make it a momentary spell. Most rego teleportation effects don't revert, the only other one I can think of is moving the image of something: and the image is constantly generated by the thing, so that makes sense.
In all honesty the Baseline is way too low, and there is no reason for a actual switch effect, to have a duration at all. Totally control a mind is 25, and this goes beyond that. Secondly, it might make sense to stipulate that the Gift and Warping are tied to the body/soul, not the mind. That keeps it from being used on any old peasant.
Side note: Not keeping moving the soul makes it a great way for unscrupulous minds to dodge their sins.
Yeah, just set the baseline to level 40. It still needs touch range, and it still needs group target, or a perdo requisite (you need to empty the targets head in order to have somewhere to put your mind). Which would make it a level 50 ritual with a perdo req, or the level 55 one without the requisite (and at that level of difficulty requisites can be really punishing)
Minor niggle: it's spells over level 50 that are automatically ritual. 50th level spells can still be formulaic.
That's why I bothered to specify a level 50 ritual 
A spell that moves you into a new body, and leaves any corporeal warping behind, is going to be a ritual.
Your phrasing wasn't clear to me.
It's not a ritual based on the guideline, or the duration or targets. The only thing that would make a 50th level spell a ritual is SG/troupe fiat saying it's a ritual, because it's too powerful. I have no objection to someone saying a spell is too powerful and it must be a ritual (a canonical example is the 40th level Neptune's Wrath, on page 125 of the main text).
Clearly the guideline should be a ritual. This is one of those things that qualifies, if anything does.
What's the qualification for a guideline being a ritual?
Guidelines generally aren't designated as rituals, the one exception I know of, of the top of my head, is Incantation of Summoning the Dead relies upon a guideline that is designated as a ritual. Some people, myself included, think that it's wrong. The only way I can see it not being an issue if you go back to the ArM4 convention that allowed spells to be cast as a ritual or formulaicly. Allow IoStD to be cast formulaicly once the ritual had been cast for any particular ghost. The first casting gives Vis to the ghost allowing it to manifest, and basically giving it Might, and subsequent summonings of the same ghost should be "free."
If it's impossible for it to be used without producing a "spectacular effect" it should be a ritual.
Transferring a mind between bodies certainly seems like a "spectacular effect" to me.
Most guidelines can be used in non-spectacular ways, so there's no reason to designate them as rituals.
How would you use transferring minds from one body to another in a non-spectacular manner?
Creating fire and lightning bursting from one's palm is the epitome of a spectacular effect. Spectacular effect is subjective. My point as been that the guidelines and rules for making spells in the metagame aspect of making spells are objective. D:Year and T:Boundary are ritual spells. If you want to get subjective, that's fine, and even clarified that if the spell is too powerful make it a ritual.