Help me to understand how RBF / double-spend work

I did the following:

1. Sent a transaction with low fee (it is in unconfirmed state)
2. To cancel it I replaced this transaction by "double-spend" transaction with a bit higher fee through Electrum. (fee is still low even increased, transaction is still unconfirmed)

At this point I don't see the 1st transaction anywhere (neither in wallet interface not in blockchain explorers). Only the the modified transaction is visible everywhere. And also my wallet balance shows the amount is back on account.

What will happen if I "finalize" the modified transaction (set RBF=OFF) and decrease fee to zero?

Will the original transaction pop-up again and there is a chance that funds will be sent finally as it was specified originally?