On the original question: “Will UE try for reestablishment on source or target or other cell?”
Depends! UE will start T311 and search for a cell for reestablish the RRC connection. Take a look here: What is the difference between timers t301 and t311? - #4 by marcengo
it can be the same cell or another, it doesnt matter, as long as the UE can reselect to it…
Now, if the same is cell is selected, unless UE-side and eNB/-side timers are not aligned, the eNB will still hold UE´s context and everything will be reestablished (SRBs. DRBs, etc…).
Now if the UE reestablishes in another eNB, this may not work and the UE may have the reestablishment rejected. Usually if the cell the UE tries to reestablish was part of the source-target pair, it will also works, but, if not, it may or may not.
If the UE reestablishes in another cell (not source or target) the new eNB will have to retrieve the UE context from the source target via X2 and I think S1 can be also used. If this procedure doesnt work for any reason, reject.