For what its worth, i dont think missing max 6 weeks or so of swimming is going to inhibit his ability once he does get in the pool. My DD#2 was your sons age when i was heavily pregnant with DD#3, thus the reason i took her out for a term of swimming....you wouldnt know it now, 10 months later. Kids learn and adapt quickly. Maybe you need a term off, it doesnt seem worth the worry...

Good luck - i know how these things can take over our lives. You will look back at all this in a week and think 'im so glad i made that decision.....