Given the uncertain nature of the exact fee to be paid for the transaction, aren't I right in thinking that there will always be some bitcoin left in the original account?

[quote
Electrum is not compatible unfortunately. Here are instructions for restoring the wallet with Mycelium: https://support.mycelium.com/hc/en-us/articles/206335729-How-do-I-restore-a-backup-
[/quote]

Thanks, but am I right in thinking Mycelium is a phone app only? I'm looking for something I can use on my PC.

Thanks, but those instructions just outline how to make a backup wallet... on Blockchain. But I'm trying to get off Blockchain.
Can anyone tell me, in very simple instructions, how to use my 12 code words to get all the bitcoin from Blockchain into another wallet, say  Electrum?

Maybe it will, but I'm not looking for reassurance about Blockchain.info, I'm looking for detailed instructions regarding getting my private keys from Blockchain. Is there not at least one person in this forum who has an account at Blockchain who knows how this is done? 

I can assure you I have looked very carefully, however I shall bow to your greater knowledge if you can tell me how it's done?

How do I do that? I have scrutinised the Blockchain site and I cannot see any option to 'Export Private Keys'
Can anyone with a Blockchain account tell me how this is done?

I have some Bitcoin in a Blockchain.info wallet and am concerned about how accesible my funds will be in the event of Blockchain suddenly going offline and the site not available. 

Let's imagine that the site is no longer there, can anyone give me the steps needed to get access to my Bitcoin? Is it even possible?