A creature can still make rolls to escape from quicksand while Force Held.
That said, if you used Turn to Stone it would be entirely unable to escape and would inevitably sink to its death.
Of course, that would take a minimum of 2xLevel for the quicksand, and 2+4+12 = 18 mana for the Turn to Stone. So for example, a guaranteed Lord of Fire kill would cost 30 mana. And your opponent could counter that with a 6 mana Dispel and a 3 mana Teleport.
In general, quicksand is a good delaying tactic but is never a cost effective way to kill something.