The problem is if he fails in TNA, WWE won't want him back for a few reasons:
A. They see that RVD isn't going to light the competition's rocket on fire, so no rush to get him back in the fold, especially when you didn't really want him back in the fold to begin with.
B. RVD went to the competition. THE COMPETITION. For someone that's looked so far down like RVD, that's going to be a killer.
Just my thoughts.
Who cares, though? RVD is like 37 now and if it doesn't work out in TNA, he's still got Japan and other indies. He doesn't exactly strike me as a "lifer", so I doubt he's planning on being in the business THAT much longer anyway.