Interesting issue of who's "first to fight" you've brought up there.
As 03USMC says, it all depends on who is needed for the job.
For example, we have our ready response (I guess they live by the same motto of "first to fight" or "tip of the spear"). They are 1 and 2 RAR (Both Light Infantry - 1 RAR has Airborne capability). But despite this role the SASR and 4RAR are often the first in anything.
So it very much would depend on the situation. It may not always be viable for the marines to be first on the ground.
As for the war being over, I don't think you'll find that'll happen to soon, and even if it has, I'm sure we'll (USA, UK & Australia) be seeing active service in a whole plethora of other places (Iran?). So I'm not to worried about a lack of overseas service when I graduate RMC, my only worry now is getting into the Inf battalion I want.