because Hive's got a little over 89 millions of blocks now

Heh. I see I'm not the only one who takes a month to write a post :oP

After the oldest part file containing initial 1 million blocks is removed, the block log is effectively pruned and full replay is no longer possible.

Technically the information is correct, but it is worth pointing out explicitly that even if you are missing oldest block_log parts, you can still replay as long as you have valid snapshot that covers missing blocks. Although personally I'd keep all parts somewhere, because snapshots are easily outdated.