I've never been too sure about this, but it has happened to me, so:
Increment - hence, in theory the game can go on forever.
Drawn position, but not trivially - e.g. there might be a fortress, but that might not be evident to everyone. In the particular case I remember I had a Rook+Bishop fortress against a queen and King but there were also pawns on the board. It was "clearly" drawn, but the point is...
the game can just go on and on and on. Three move repetition need never arise ; the 50 move rule (does that even still exist) need never arise (or at least not for many hours) as the odd pawn move can always be made, and any 2 minute rules can be kept at bay by the increment. So...what exactly is the protocol?
In my case, I did call the arbiter (it was 22:30pm and I wanted to get some sleep), but even then it took another 30mins and probably only ended because the other player did eventually concede the draw- probably only due to my demonstrable frustration and having to pseudo repeat moves.
In short...is there an issue here or am I (and I suspect a few others) just ignorant of the correct protocol?