10000 addresses?? Don't understand why you created so many addresses but I say just back up the keys to a secure location first then do it with 100 addresses at a time in electrum. Can't think of any other way.
Yes, already did it, many thanks for responses! It was damn painful )
Also beware: If you have 10,000 addresses and you're trying to put them into one, I'd assume you have 10,000 inputs... just your inputs alone would be over 1.8 Megabytes... which is larger than the block limit!!!
you will need to bunch your bitcoins together in transactions of less than 100 kB... which by the way, would be at the most 552 inputs and 2 outputs.
So if I were you, look at all the utxos you have, and bunch them together in groups of 527 inputs and send them to another address (so 1 output) and be sure to leave AT LEAST 0.00096 BTC miner's fee. (literally, anything less than 0.00096 BTC for a 96 kB transaction and it will be treated just like a no fee transaction...)
Any transaction over 100000 bytes will not do well...
if you have 10,000 utxos and put 527 in each transaction. you will need 19 transactions to pool them together in one address, then you'll be left with 19 utxos... if you want to pool those together 1 transaction is ok...
So your endeavor will require about 20 transactions to do.
Good luck, and have fun ;-)