Let's asume I make a transaction with no fee and doesn't get confirmed after a while (let's say 10 days).
Could it be confirmed after that if for some reason some miner keeps a copy? I don't ask if is likely to happen but if it is posible.
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Absolutely. There are cases of transactions remaining unconfirmed for several days and then getting confirmed.
If the transaction was ever broadcast and is still valid, it can be included in a block by any miner who wishes to include it.