Yeah, the only problem is that... they might... switch...KOing Desukan isn't necessary :)
But if you switch after their first hit on Deathkan, then it's not very likely that they'll switch on that turn, as they'll want to keep orking on killing Deathkan so that he won't be able to Mummify anything else. And once Slaking is in, they can't keep him from getting Mummy.
I only wish that Regigigas could learn Pursuit.