Jagielka will obviously have more lucrative offers than Utd's if money is his main driver. However, given that he's already a multi-millionaire, would the challenge of returning to Utd appeal more that a move to say a move to Sunderland, especially if a coaching aspect (badges, future role etc.) was included in the offer? He knows the club well and the opportunity may well suit him if he is indeed looking to move into coaching/management once he finishes playing.
I'd say it is still a long shot at this stage as it apparent from some of his recent performances (e.g. v Man U) that he's probably still good enough to play at Prem level in some form (even though he's lost a yard of pace), which would obviously favour clubs such as West Brom, Palace etc. However, if CW and the club can persuade him, it would be a huge signal of intent and I personally he'd be a great success, orchestrating things in a back three alongside JO'C and Basham/A.N.Other (Webster?).