As 'unfair' as it is, the games won't have any supporters in so I don't see how they can retain the credits. If someone bough Palace, Burnley, Villa & 1 other game this season you think they should go into the 4+ ballot for next season when only one of those games was actually played? Nah.
That's just my thought though and I doubt it'll even be what happens.
But those people have done the "hard work" and got those tickets and presumably would have gone to the games, it's not their fault they might now not get to go. If those are taken off them then they're back down on 1 with people who either hadn't managed to get any more, hadn't bothered trying or weren't going to and were happy with just the 1 credit.
I'm on 19 (or 15!) so it possibly doesn't really affect me but if I was on a lower number and it meant I'd be dropped to a lower bulk sale level when I'd worked my arse off to get tickets and then got fucked over by a virus outside my control I'd be devastated. If I was on 4 that I'd attended, like you say above as an example, I'd honestly be happy for those with 4 but who had only been able to attend 1 to still count as having 4 as I'd know they'd put the work in to get those tickets.
Like you say though, whatever they do will upset half of us! Your point of view all depends on how lucky you were in the bulk/late sales I imagine!