The trans will not fail due this blower swap. Ford builds them tougher than that.
It may not go 250K miles as designed with the addtional boost/torque, but it's not going to outright fail or a long time due to the extra torque. It really depends on the driver more than anything else. I know a guy who tends to destroy evertything he drives wheter it's stock or modified- he abuses mechanical things for fun while saying he's extracting maximum performance from it. Not my money so I don't really care what he does with his stuff, but it goes to show.