I show him this:
Generators store and return 64-bit values in all versions of Firebird. This gives us a value range of:
-9,223,372,036,854,775,808 .. 9,223,372,036,854,775,807
So if you use a generator with starting value 0 to feed a NUMERIC(18) or BIGINT column (both types represent 64-bit integers), and you would insert 1000 rows per second, it would take around 300 million years (!) before it rolls over. As it is pretty unlikely mankind will still walk on this planet by then (and still use Firebird databases), that's nothing to be really worried about.
So there. No worries about running out of numbers.
He acknowledge this. Then we saw that the application not only shares the sequence numbers, it jumps 100 when the server is restarted. He said that it's a waste of numbers. Again, I reminded him of the article. He still not feel comfortable about it. So I gave him this analogy:
You are not a rich man. You are used to getting the most for your money. You tried to get a good bargain for everything you buy. You evaluate if you really need it. You tried to look for cheaper alternatives.
Then you met a rich man. He never bargain. He doesn't look for cheap alternatives to what he want to buy. He just get what he want with no second thought. You know that the money spent is chicken feed to him. He can use his time looking for bargains in more "meaningful" stuff. But that will not stop you from feeling the "waste".