What happens when DB engine runs out of numbers to use for primary keys?

Question

Since DBs do not reuse numbers of deleted records it is possible to run out of numbers, especially if you pick not really a big integer type for this column.
What would

Answer 1

Yes it is possible: if you only allow for 2 digit numbers you can only have IDs up to 99, and so on. Inserts would fail once the limit was reached. It is a matter of common sense to choose an appropriate size.