Voice acting for a one-off game? Yeah, it's possible to see a 2 year contract - you'd expect Ben Starr might have had a longer contract for FF16 because they knew the scope was going to run into the hundreds of hours.
But for something like this, the contract will be for the exact amount of studio time. So they'll know it's roughly 4 sessions of 4hrs for that character in X Expansion, for example, and they'll make a contract for that for the, say, one week those four sessions will take place. There'd usually be some stipulation for additional time, with a per hour rate, but we're talking a single extra session or running over by an hour or something. If they need the actor again, they'll set up a new contract when it's time.
A rolling contract would be considered too restrictive if it was challenged in court, because it would prevent the actor from taking other work (non-compete clauses are largely meaningless here, as are overly restrictive contracts that could prevent someone working) - being tied in to some maybe-date in 18 months' time for a single VO session preventing them from taking a six-month gig filming for TV or being in a play, for example.
Anyway that's probably far more detail than anybody needs, I just either know nothing about a subject or everything
