The secondary looks like this in September:
CB - Talib
CB - Rogers-Cromartie
FS - McCourty
SS - Pollard
If they pulled this off, would anyone really miss Welker that much? This would make them a top 10 defense easily, and they'd still be a top 10 offense.
I'm not suggesting this is exactly what is going to happen, but don't be surprised to see them re-sign Talib and get some more help in the secondary, which would include another corner and a hard-hitting safety.