I'm no expert on salary cap and hits but AFAIK the only salary cap penalties for cutting a player are his bonuses. Baas has workout bonuses each year of his contract for 250k. Cutting him after this season would then result in 750k cap penalty. Well worth it considering his 2013 cap hit alone is 6.2 million.
Sacks alone do not determine whether an offensive line is good. Eli himself is a big reason for this. A more telling statistic would be amount of QB pressures allowed.
Wouldn't cutting him accelerate his signing bonuses as well? Those alone wouldn't make him likely to be cut.