1. 1. Do you think there's still time for them to return & feud?
Not really. There are only three more episodes of Raw until WrestleMania XXX and all of the prime spots are taken or will probably be taken by the end of Raw this Monday.
2. 2. Will only one of them return? Who could they feud with??
I'd say that there's a possibility of one of them returning, but I highly doubt both of them will. If I had to guess which one would return, it's RVD. Chris Jericho is doing his own thing right now, or he was the last time I heard anything. There's not really enough time for either one of them to partake in a real feud for WrestleMania at this point. If one or both do show up, I think they'll show up as surprise entrants for the battle royal.
3. Are they needed for WM?
Not at all. Generally speaking, most of the focus going into WrestleMania will be on Taker vs. Lesnar, Bryan vs. Triple H, Bryan possibly being introduced into the WWE WHC match, Cena vs. Wyatt, whatever goes down with The Shield and some holding out hope that CM Punk will pop up in some sort of role. These matches will probably be the ones given the most time, if I had to guess. Given how their WWE returns have been in terms of their schedule, it's not as if their addition to any sort of championship match will mean anything. RVD works for 90 days and then takes off for an unspecified amount of time. Last I read anything, he reportedly stated he'd be back in time for SummerSlam. As far as Jericho goes, he's great to have but his role is almost always restricted to putting over other guys.