gettransaction for a tx that was sent with RBF shows "bip125-replaceable": "no".
Is the flag reset once a tx gets into a block?
Yes (basically). Once a transaction is confirmed, it is, by definition, no longer replaceable under BIP 125, therefore the field bip125-replaceable will say "no".
The current way is more confusing, as one expects the command to interpret the bit data of the transaction.
There's actually a bit more to whether something is actually replaceable than just the signalling. That is included in the checks for labeling a transaction as replaceable.
Knowing that RBF can't be used on txes already in a block seems self-evident? Especially to people who would use commands to check it.
Just because a confirmed transaction signals it does not necessarily mean that it was actually replaceable when in the mempool.
I moved it for you, but next time, do it yourself (OPs can move their threads) or use the report to moderator link.