Full RBF

[LoyceV]

And in such case, most of the stolen coin goes to miner as TX fee.

That's the beauty of it: it makes hunting compromised private keys futile

[satscraper]

The transaction B must pay 1000 satoshi more for its own bandwidth and since the transaction A paid 500 satoshi, it should pay at least 1500 satoshi in total.
So, as mentioend above by BlackHatCoiner, the fee rate for the replacement transaction must be at least 1500/1000 = 1.5 sat/vbyte.

Wow, completely forgot about A.   Nevertheless that is not a rule punctually kept. Miners may  accept and include into block transaction with the feerate literally equal to zero. They do it sometimes when this involves either  their own transactions (RBF included) or payment receiving (in cash for instance) outside the blockchain.