That sounds like a lot of things would need to go wrong all at once !

I've flown out of BKK on QR a few times and check-in does not close 3 hrs before departure. It may open 3 hrs before, but it closes probably 45-60 mins before. And there are separate desks for first, business and online bag drop.

Yes, there's a slim chance online check-in may be down, but it opens 36 hrs before departure, so it would have to be down a for long time. And delays getting to the airport ? That's what travel insurance is for.

Check the specific fare rule, but no-show fees are usually chargeable if you fail to cancel one hour before departure. Sure, you'd need to pay the change fee and any fare difference, but the no-show fee is avoidable unless you're really sick, etc. Running late ? Call from the taxi.