This is why you need to make backups of your private keys/seed whenever you're generating a new one to prevent something like this from happening.
Backup seed (or private key) is a MUST.
Another step that is forgotten by many people is: Don't test validity of backups, by that I meant they make backup of seed (or private key) but do not test its validity (correctness in other words). Do not make a recovery trial from such backup. If the bad case when they write down some words (with seed) or some characters (with private key) inaccurately, they will get big troubles later when they must recover their wallets.
Create wallet
(offline) > Backup (seed/ private key) -- do it
offline > Copy the backup to multiple devices > Store backups safely (water-/ fire-proof) > Always test backup's validity.