If it's the same version as mine, the 6 inch capacity simple one with a 64+1/2 inch long 1/2 inch wide blade, then my experience is that once the blade has come off it'll never run true again. However before fitting another blade, check the wheel alignment with a straightedge in two planes just to see they're somewhere handy.
Unless something has changed (bearing collapse, frame twisted or something major – but if so why is it not obvious) then you should be able to get the new blade to run in the correct position reliably just with the two wheels aligned by eye. . Twiddling the blade alignment screw (tracking adjustment) from this initial visual wheel alignment shouldn't make the difference between keeping the blade on and having it jump off, though it can make the back of the blade ride up the ridge on the wheels and that ruins the blade. Guess how I know!
The blade should run with the teeth off the front of each wheel – I've found if you let the blade ride onto the wheel too far you iron the set off the one side of the blade and then you're on a hiding to nothing.
HTH Simon