If I was to send myself payments to this address and in 5 years for example -- I would place wallet.dat back into another Bitcoin wallet, would it catch-up and find all the payments that were ever sent to that wallet?
Yes, it will catch up.
IMO,
5 years of time, the HDD or USB stick could be corrupted in hardware level. Low probability but could happen.
Preparing 2~3 USB sticks and storing identical wallet.dat file will be safer to keep it long. Also, check both USB's condition once a month, by mounting onto "linux or mac, offline computer" I wouldn't consider windows as a safe computer.
Lastly, if you encrypted wallet file, 5 years could be long enough time to forget your own password. There's no such thing as "reset password". Be very careful not to forget.
I appreciate the response. This pretty much answers my question. Yes, of course multiple immediate copies on multiple external storage. Perhaps even burning a copy of wallet.dat, a copy in .rar and .zip of the same file over multiple dvd copies would achieve the same purpose.
What about code changes or even "forking" as I have seen with some Alt-Coins. Does that not require some changes to the wallet.dat to remain valid?