I doubt the Sox try to carry both Slaten and Mata, unless one or both are just flat out dominant. There are options, one of which I expect (not counting placing one or both on IL).
1. DFA Mata and re-sign him if he clears waivers. (The Ol’ Slip ‘Em Thru Waivers trick)
2. Complete a trade for Slaten. Or a financial transaction.
3. Trade one or both elsewhere. (Least likely.)
Not sure what other options they have but there are probably a couple…