Let's say we pencil in the following for the moment:
LT - Bakhtiari
LG - Sitton
C- Tretter
RG - Lang
RT - Bulaga
Barkley would certainly be kept as a cheap, versatile and credible RT and G backup.
Under this scenario Bulaga would be the backup at LT if Bakhtiari is injured with Barkley sliding in at RT. Lang might be the emergency center again, with Barkley taking his spot at RG in that eventuality.
Under a 7-man scenario, which McCarthy has used more often than not in recent years, there's one spot available. That spot could go to a guy who can compete for the C spot or at least back up. That could be as simple as keeping Gerhart on the 53 man roster.
I think the 8-man scenario is more likely as the pre-draft default position given that Bulaga, Sherrod and Tretter have question marks and the team has no idea what they have in Sherrod until training camp.
I could easily see one pick expected to compete for the C/G spot penciled in for Gerhart above, or even compete for starting C. I could see a second pick going to one of the patented Thompson/McCarthy college-LT-converted-to-interior guys in a middle to low round if their pre-draft outlook for Sherrod is not encouraging.
We have other names on the roster now: Taylor, Tiller, Adams, Vujnovich. These are "just guys" as is Gerhard, but the team might roll the dice betting one of them will progress to serviceable backup status for at least stashing on the practice squad.
I think the odds we draft 3 O-Lineman are probably lower than our drafting none at all. One in the 3rd. - 5th. round and perhaps a second in the 5th. - 7th. round are the more likely scenarios.