More than likely as individuals, what they choose to do. Plant is still in the biz, Jones produces and plays. Page I haven't heard much about lately.

Plant has his own band, his recent album got good reviews but IMO its average, I guess the critics gave him bonus points for it being different.
Jones is a real class act, like filstan said he still plays and produces.
Last I heard of Page was his tour with the Black Crowes, which gave us the great "Live at the Greek" double CD.
Anyways both are bloody great bands, but although Bonham was a great drummer, he ruined some songs because he had no restraint and overplayed, much like Page did (live). If you listen to Black Dog, for example, the outro solo is amazing in the studio version, but most live versions suck, because there is no rhythm guitar and its mostly wank. Anyways besides being rock bands based in the blues, Led Zep and TRS are completely different.

Robert Plant had a concert in my town, about 2 years ago. I even met him down by the bay, he was walking around real quitely. Strange that big artists, come up here sometimes. Quite frankly, the concert was not something I'll remember. He looked very old, very much wrinkles.