It appears my explanation was bad, very bad. When I said "It gets re-cached only if someone -- or something -- accesses it again", what I meant was "It gets re-cached only if someone -- or something -- accesses it again -- and if the cache file is older than the value of $translator_cache_days." Does that make more sense?
The largest site I'm translating is around 3k pages. If you're translating 20k pages, your servers IP will get blocked and unblocked for months while the cache gets built. The only method to get around this is technically complex and requires a dedicated server.
The pages I had removed only got reindexed when I changed their URL's. I implemented a subdomain model instead of a subdirectory model. It's complex, but it's working. Traffic to those translated pages is only 1/3rd of what it was. I'm not sure if I should assign the cause to the loss of inbound links due to the deindexing or if I should start thinking that subdomains don't transfer domain authority as well at subdirectories.