Since GPU farm is worthless, 71 has almost no chances of being solved this year. Maybe in next years, unless someone is very lucky or the price goes to 200k.
And about withdrawing the funds. Mara is the only option right now, either you trust it or not.
Once a transaction is confirmed by a miner, there should be no more funds in the source address that a bot or anyone else can resend at a higher fee, right?
Yeah, once mara got one block mined there will be no longer any funds in the wallet and the process is irreversible. I've made a tutorial of how to withdraw the funds safely throught Mara. But in a nutshell: the coins remains in 71 till mara mines a block, until that the public key remains not exposed.