This is too far from happening here in my country but not impossible to happen. If they can implement this bitcoin as a payment then paying on restaurant is much easier and it is just like credit cards. Unless my country fully utilized the benefits of bitcoins then it will be a bigger help in other industries as well.
I don't think it will be much easier to pay in bitcoins on restaurant cause as you already know we are having a problem with confirmation time . Paying in credit/debit card takes a minute but bitcoin takes at least 3 minutes to confirm a block assuming that you pay a high priority fee . If the miner fee and confirmation time didn't improve itself, restaurants accepting bitcoin might be difficult to make it happen .
It can totally have an issue just like that if you are gonna pay directly with bitcoin but I think they are aware of this problem and will think ahead of a solution for this kind of problem, but if not it is still OK if you convert your bitcoin with Fiat then your problem is solve, but regarding some restaurant or merchant that will accept bitcoin I think they have a solution for this!