If Kirstie Alley couldn't come back, then who would you have cast as Saavik instead of Robin Curtis?
One suggestion that I read on TrekBBS was Joan Severance, but I don't think that she was actively acting at the time that The Search for Spock was being produced.
https://www.google.com/search?q=joan+severance&sxsrf=ALeKk03fyr0vY4dFuELGph1JJyK-pWoPMA:1603620722392&source=lnms&tbm=isch&sa=X&ved=2ahUKEwj6uIzcwM_sAhUSGKwKHRf_AjYQ_AUoAXoECA0QAw&biw=1600&bih=732
And yes, I bring this up because of the criticisms about Robin Curtis apparently being miscast as Kirstie Alley's replacement:
https://www.amazon.com/hz/reviews-render/lighthouse/B00006G8HX?filterByKeyword=robin+curtis&pageNumber=1
https://www.trekbbs.com/threads/so-who-did-the-worst-single-acting-job-in-the-first-10-films.266536/page-2#post-10792633
https://www.theviewscreen.com/star-trek-iii-the-search-for-spock/
http://www.100share.com/zz6300214400.htm
http://secretvortex.com/strek3-sfs.html
https://www.trekbbs.com/threads/st3-why-i-love-it.283376/#post-11748379
https://www.trekbbs.com/threads/missed-opportunities-in-the-tos-movies.286986/page-3#post-11975778
https://www.trekbbs.com/threads/how-much-stock-do-you-put-in-the-even-odd-curse.300948/page-2#post-13079805