I would overjoyed to see people back since their deaths depressed me so, but here's the issue. Lee is dead. Your not him anymore. The whole reason they were good characters was your (lee's) relationship with them. For better or worse you would have lost everything you had been through with Kenny.
Carley is another popular suggestion and telltale could turn around and say "it hit her in the cheek then a passing doctor saved her life" if they feel like it, but the bond you had wouldn't be the same.
You can bring the characters back but the relationships can't be revived.
That said. A little cameo or Easter egg hint they might be OK would make my week.
Edit: or a flashback/nightmare sequence if you play as Clem could work as well
BFF's: Lee, Clem, Carley and Kenny
Although the forever in BFF should be taken loosely