In case Electrum as a wallet/code/program dies and stop being updated etc. - are my bitcoins still safe? Will my private keys created on Electrum still be available for use on different platforms?
As no one seems to have addressed this concern as yet... private keys are really just very large numbers. They are NOT wallet specific. A private key generated by WalletA should be able to be used by Wallets B through Z (assuming of course that these wallets allow importing of private keys).
There are also several open source and freely available services (like bitaddress.org) that will "convert" private keys in multiple formats to (WIF, WIFC, HEX, B64, B6, MINI, BIP38) and output WIF, WIF Compressed, Hex and Base64 representations of these private keys... They provide full sources and are able to be downloaded and run on airgapped/offline machines etc.
The maths and algorithms behind all of the address conversions etc are also widely known and published.
In the specific case of Electrum, which uses a "proprietary" mnemonic to seed calculation method (ie. Not BIP39)... if you're super paranoid that the software may die and/or stop being updated... you can also simply store a copy of the source code or application on your secure pendrive along with your seed/keys...
or alternatively use the getmasterprivate() command on the Electrum console to get the BIP32 Root Key aka "xprv" (that can be plugged into an offline copy of
https://iancoleman.github.io/bip39/):

and used with a BIP32 derivation path of m/0 and m/1 to get your "receive" and "change" address/keys respectively.
