I do not have experience in this special case, but to me, replacing the deck on a Searider seems to be a tough job. When i look into the hull through the big hole at the transom, it looks pretty weird. Not the classical hull-stringer-deck system.
If there really is a marineply core in the deck laminate, you are right, i also would be concerned about the plywood.
On the other side, if they really replace the deck an do a good job, why not? Then you have a great boat with new tubes and a new deck.
BTW, if you eventually will have some photos, i would be VERY interested to see the work on the searider deck an how to replace it.