I've never used tunnelers I have to admit, been thinking about it, but I always thought that scatter rule makes it just a bit too unpredictable.
But from how I interpret the rules I would say:
1) Reading it literally, yes, troops would be destroyed since they are off table. BUT, with that said, that just sounds too harsh and maybe something that was overlooked in the rules. I would probably, with my opponents approval

Implement a house rule stating they would appear at the point where the table stops, and go with that.
2) On this one I would say no, if what you meant was, can the Tunneler itself engage an enemy stand in CC that is inside that area where the tunneler ends up (after scatter). This because the tunneler rule says that: "
A tunneler may fire its weapons in the Advance Fire Segment on the turn it surfaces."
Too me that indicates someone has thought about what it should be able to do once it surfaces, and that is basically only that it can fire in the advance phase.