All organizations have a disaster plan in place and this is one scenario they no doubt have contingencies for.
What would the plan be? In terms of competitive realignment or modifying of rules I suppose you're referring to.
First, it would probably depend on which team/divisions are affected. Of course this team's opponents might have one less game on record, depending on when the crash occurred. I have a hard time seeing the NFL dropping games in order to equalize game counts. So, maybe just go with overall record percentages for that yr, and look to realignment going forward.
Then you might have some type of expansion-like draft in order to create a replacement franchise in the coming yrs. The ownership would still have all the legal rights under the Charter to have a team, so I'd would expect he/she/it(Snider) would want to carry on.
That's a rapid reaction, but yeah, it's interesting and I've allowed that to enter my thoughts in the past as morbid as it is.