I think i would reject.
Right now you have a pretty balanced roster...if you trade Longoria you will leave a gaping hole at 3B, with only Rolen to fill it.
It would also weaken your RP a lot as Ryan is really the only one with a stable job.
In return Soto is pretty similar to Mauer (although his back injury is a concern), which makes it really Longoria and Ryan for Lincecum, and while I like Lincs a lot, your SP is not really that much of a weakness, although you have very little depth, compared with the downgrades at 3B and RP outlined above.
Surely there is a better 4th pitcher than Schmidt available btw?