Section 12 of the CBA deals with leaves and returning from leaves - that might be a good place to start reading. The OP didn't make it clear if the question was forward or backward looking, but:

If out on LTD, a pilot can participate in the bid process as normal but obviously won't be activated and trained until returned to the line.

If a pilot hasn't bid a new position via bid announcements or the displacement process while on LTD, and, the bid position he left still exists, he'll go back to that bid position. In other words there are no "makeup" bids just because you were on LTD.

Again, read section 12.

Regarding the PDR, I get an accurate and timely response every time I use the system, I must be the only one huh?