Hold the tx1 and broadcast tx2, if successful broadcast tx1 if not go to another mixer
That could be made with 1 or 2 or 8 block away between tx1 and tx2 in this example ?
I can't assure what is your point, but there is no pending in network.
If a tx is broadcasted, it will be included in a block with priority of fee.
Hold the tx1 and broadcast tx2, if successful broadcast tx1
Is this meant spend first then take input ?
User can monitor whether tx2 is included in a block(whether real payee is paid).
And tx1 is not broadcated yet, user can make a another tx and broadcast it.
Send coins to his news address.
There is a method to delete unconfirmed tx in wallet.