It is entirely possible to lose it, but don't count it out yet, it'll probably find a bunch of mark 1-4s fleet ships on the next planet and heal itself up. The only way to truly kill that thing is hope it runs onto a mark 5 only planet. Which is rare.
Which no, its not weak, wait till you run into it with your fleet of 2K ships. Never seen a fleet like that die so quickly....*shudders*
King