Here's a story - my brother took our boat over to barrier towed behind yacht - lost on way over recovered 2 days later upside down only bow visible - as over in barrier he rang boat shop - told to remove plugs fill with fresh water turn over by hand and then same with liquid wd40 - then as soon as able to (took a week as electrics melted) run motor under load (on trailer in gear) to get warm. Ran for 2 months, developed a rattle then threw a rod out crankcase - when stripped down crankcase full of rust!
I think what he should have done (and didn't want to ) was immediately strip motor and clean out - if you have this done you should be ok - but like you say what happens in 3 months time? Sounds like you may be ok but I think if you decide on strip and clean only you want a guarantee in writing (which they probably wont give) from insurer or shop if anything goes wrong down the line.
I would insist on replacement for peace of mind....but I am sure insurer will wriggle on this?
Good fishing trip nothing breaks, great trip catch fish.