I think just jump in. There's no rule that says just because you took a lead, you can't take another. Some are happy just playing rhythm, others want to be out front. I don't think it matters, just don't let the tune die or ramble on. If no one takes it, just jump in. Some are happy just playing rhythm, others like being out front. It has alot to do with player skill and comfort level.
Lets face it, when you take a lead, for that moment in the tune, you are out front, and everyone is watching. Look at your lead guitar players from some of your favorite groups---they are usually the most wired guys in the band, and love to be noticed, while the rhythm player is happy to just be in the back somewhere, driving the song with the drummer and bass player. It is what it is, it depends on the player.