Boyes absence doesn't directly lead to signing Ryder and the B's certainly were not "forced" to sign him. IIRC, Ryder played for Julien in Montreal, so that connection likely influenced him being with the B's. Ryder had 2 consecutive 30 goal season before last year, in which his role changed significantly.
The returns so far on Ryder are not spectacular, not for the $ he's being paid. However, that signing has nothing to do with the trade of Boyes, per se. You might argue that it has more to do with Glen Murray falling off the map.
BTW, Ryder is a +7 thus far, so while he's not lighting the lamp, he also is not killing the B's with crappy defense and lousy effort.