A team needs 4 full time QB arms in training camp at a minimum, so the question isn't if the Panthers will add a 4th QB, but how they will do it?
1. Draft A QB (in the late rounds) - Anythings possible, but the Panthers don't have enough picks to fill all their draft needs as it is.
2. Sign A Free Agent QB - Unless it's Dennis Dixon (a QB simular to Cam's skill set), I don't think so. The Panthers already have Derek Anderson and Jimmy Clausen as Cam's backups, and unless they trade/cut one of them, any 4th QB is only looking at the practice squad as his best result.
3. Sign A UDFA QB - This is by far the most likely option.
The Panthers have mentioned a couple of times that they would like to have a backup QB with the same type of skill set as their starting QB, so that they can run Cam's same offense if the backup QB had to enter the game. Neither Anderson or Clausen have any run ability like Cam does. Even if the Panthers were to try to switch WR Armanti Edwards back to QB, he doesn't have any practie squad eligibility left (he played in too many games last season), so to keep him on the 53 man roster, either Anderson or Clausen would have to go, or he would have to remain their 5th or 6th WR. So I believe they will just sign a UDFA backup/practice squad QB, but who?
I believe the best UDFA QB option is ECU"s Dominique Davis (6-2 3/4, 221, 33 5/8 inch arms, and 9 5/8 inch hands). He's only average height, but the only QB at the Combine with longer arms was 6-6 7/8 Brock Osweiler, by only 1/2 inch. Davis had a great Pro Day workout, running a 4.58-40 (same as Cam's best "unofficial" 40 time), a 6.93 3-cone drill (Cam's time was 6.92), a 4.27-20 yard shuttle (Cam's time was 4.09), 15 bench reps, a 36 inch vertical jump (Cam's 35 was an inch shorter), a 10-4 broad jump (Cam's 10-6 was 2 inches longer, and an 11.26-60 yard shuttle. So, you can see that his measureables are almost a carbon copy of Cam's, but more important for the Panthers purposes, he's ranked in the low 400's on most draft boards, over 150 slots out of the draft's best 253 draft picks.
Davis passing numbers at ECU also remind you of Cam, except that he didn't run very much, in spite of his 4.58-40 speed. Here are his passing numbers:
2010 - 64.5% - 3,967 yards - 37 TD's - 16 ints - 141 rushing yards
2011 - 67,6% - 3,225 yards - 25 TD's - 19 ints - 172 rushing yards
As you can see, his biggest drawback is the number of ints, but remember the Panthers wouldn't be signing him to be Cam's backup this season, but maybe the 3rd QB in 2013, after a year on the practice squad. Davis now holds the NCAA record for most consecutive passes completed in 1 game, with 26 against Navy, and also over a 2 game stretch, with 36 straight completions. Another plus for Davis is that he should very knowledgeable about how the NFL works, as his older brother is Bears TE Desmond Clark (who attended Wake Forest).