Hi,
Quick question that may have been answered before, or is just really dumb:
Is there any hard limit to the number of light wounds a character can sustain before dying?
-A
Quick answer: no.
In Ars Magica, it is not possible to die from 100 paper cuts. This is probably a good thing.
It is also not possible to die from a million paper cuts. This is...less clear cut, shall we say?
It's worth bearing in mind that those light wounds will usually have an effect on the damage you take from future wounds, either by decreasing your defense total (and therefore increasing your opponent's attack advantage and therefore damage done), for combat damage, or by acting as a penalty when soak is rolled for non-combat damage. (Soak isn't rolled for combat damage, so the penalty only applies once.)
An exception is Perdo Corpus spells to cause Light Wounds, which will never cause anything worse than a Light Wound, no matter how hurt you already are.
One final consideration is that you need to make a Recovery Roll for each wound you take. If you have a million Light Wounds, (at least) one's going to get infected and deteriorate enough to kill you, pretty much regardless of the bonus you have to Recovery Rolls.
Thanks for the fast, and excellent answer.
Am I also right in assuming that a character with say five light wounds needs to roll a Recovery roll for each wound at the start of combat, but not every round of combat?
It's not actually completely clear.
What is clear is that you don't need to make any Recovery Rolls to avoid wounds worsening in the same combat as you took the wounds.
In you get into another fight later, the rules just say that "Any character who does more than his injuries allow must make an immediate Recovery Roll for his most serious wound." So in this circumstance you're just rolling once for all your wounds (as opposed to for each of them, when you're trying to actually recover from them), but it's not specific whether it's per round or per combat. My own inclination would be to go per combat, but I haven't tested either option out, and ultimately it's going to be a matter of troupe discretion.
Hmmm, interesting.
But magi have to roll for Recovery when the get fatigue from casting, right? That reminds me; do you have to roll for fatigue every round of combat? (I'm guessing no, unless you're fighting in snow or mud or something...)
No: "Combat and magic use have different rules for Fatigue loss that replace those given here [meaning rolling to see if you lose a level]" (AM5 p.178, Short-Term Fatigue). Basically, for combat, you only lose Fatigue if you choose to exert yourself, trading a Fatigue level for a bonus equal to your Combat Ability for one roll (see p.173).
As Halancar said.
If you did exert yourself in combat whilst wounded from a previous fight, I'd require an extra Recovery Roll then.
Thanks again for the answers. 
And at the risk of stating the obvious - don't be a slave to the math.
If the situation seems to call for SG creativity to keep believability and drama both on acceptable levels, then by all means bend the rules as you need to.