3 possibilities as to what happened...
As has already been mentioned - asteroid strike - well it IS currently smack-bang in the middle of the asteroid belt.
Not all that likely though, because as Bruce says - it's been successfully passing through the asteroid belt for literally eons - and asteroids aren't nearly as close to each other as Sc-Fi movies etc would have you believe.
Asteroid near-miss - more likely than a 'strike'.
Many comets are not one solid lump, but are a conglomeration of smaller pieces, held together by gravity, with the gaps filled in with loose dust/gravel/ice.
A near-miss could cause some pieces to move relative to each other, dislodging the loose 'packing' - which has subsequently 'outgassed' to form the huge coma that we are seeing now.
(That coma is actually larger in extent than Jupiter
)
Third, and most likely cause is a collapsing 'sink-hole'
As I said, many comets made up of smaller pieces, but sometimes the gaps aren't completely filled - these gaps are 'sink-holes'
If one collapsed, you'd get pretty-much the same effect as a near-miss by another object.
Holmes has done this before - in 1892 - in fact, it was the 1892 outburst which made it prominent enough to be discovered by Holmes in the first place.
And as for what will happen to it - well, the coma is already beginning to be blown away from the comet by the solar wind, creating a (currently very dim) tail. The main body of the comet itself, will continue to orbit, the same way it alwasy has.
Even if it breaks up - the pieces will all still pretty-much follow the same orbit that the original comet had.
Comet Schwassmann-Wachmann (SW3) broke up last year - all the pieces continued merrily on their way - following each other, all on a fairly similar course.