Depends on the airline, their contract, and their training program.
I'm at a certain Ft. Worth based regional that's about to have its name changed in 2 weeks, and it goes something like this.
You can come back to whatever seat your seniority would hold. There are 3 requal courses if you come back to the same equipment. The length of the course will depend on how long it's been since your quals are expired. Expired more than 1 year, and you go through the full long course. If you're not expired, you jump right back in as long as your landings are current. If the landings are expired, you go to the sim and get 3 landings, 1 to mins and 1 single engine plus a V1 cut (I believe).
You get a PC, a line check, and/or supervised line flying depending on the course you require and whether or not the PC/LC are expired.