i think you might be overlooking an even more glaring issue potentially. lets say you use some software to encrypt your data. then 15 or 20 years later you need to decrypt it. you might not be able to find a computer that can run that software anymore. and you might not even be able to download that software since the company went out of business. so not only would you need to store the encrypted data, you also might need to store the software and a machine (operating system) to run it on.
Veracrypt is FOSS, so you would
hope that either it or a fork of it was still available, but as you say there is no guarantee of that. If not, then provided you use a standard encryption algorithm such as AES-256 there will be other software around which can decrypt your files. If you use one of Veracrypt's cascaded algorithm such as AES-Twofish-Serpent on the other hand, then you might run in to problems if there is no other software which will run these algorithms in sequence and you don't have enough technical knowledge yourself to make it happen.
i don't know what the solution to that is but it does seem like it could be an issue.
Write your seed phrase down on paper, or engrave it on metal as this thread is suggesting.