on an experimentation roll, disaster, explosion: Is vis considered a valuable object that you need to check to see if it survives?
details on what happened will be given after our next session.
I would say that a lab explosion can destroy anything, but to roll for everything would be a waste of time. So just roll for those items, that your character finds important/valuable, of which I would say vis is certainly one of it. But also cheap but personally important items I would roll, like the little something you got from your mum when you left home....
More often than not I would say, it is the Vis which is the source of the explosion anyways (certainly the power of magic getting out of control at any rate) and thus should be deemed "up in smoke", as it were, unless perhaps one has a significant stockpile in some other portion of the lab. In the latter case I would say roll percentiles perhaps to determine how much is unaffected (as one possible scenario).
One's familiar and or apprentice (not to mention one's own person) should be rolled for, being the most valuable things in lab IMO.
Huh.. I always thought the most valuable thing in my lab was the back issues of 'Hermetic Times'. They have all the latest Vis sites and newest spells...not to mention 'Miss Tytalus'
Hmmm and I always took you for more of "Corpus Cabaret" collector
Most plague-afflicted girl of the year? 
She's the Lepers' Choice!
So here was the basis for the question...
figured ~10% of the vis was consumed and that fueled the creation of the creature that threatened the entire covanant.
That seems like a good way to resolve the issue. Could your magus survive 89 points of damage, or did I read that wrong??