This info comes from a Nintendo customer service rep, so take it with a grain of salt. We've seen them provide spot-on info in the past, and info that was completely incorrect.
According to one Nintendo customer service rep, your Switch cloud saves aren't deleted immediately if you cancel/let your Switch Online subscription lapse. Apparently there's a grace period before deletion, but no specific details on how long that period is were given. In other words, it's still going to be a gamble, but there might be a chance you can hang onto your saves if you re-up your subscription soon enough.