I agree with what was said above.
Calling and hinting that a character knows vital info was just poking the wasp's nest. The corp might have been fine with the betrayal, and having the character on the run, but now that at least one of them has basically threatened revealing secrets, they can't be allowed to live.
How far does this go in the corp? Is their supervisor trying to advance in the ranks? Can this info hurt just him, his division, the entire Corp? Chances are, the entire Corp would be somewhat fine, but any info might hurt this particular Supervisor's chance at advancement. Think Robocop, Dick Jones is trying to push the E.D. 209, but a public execution in the board room makes the CEO decide to give someone else a chance to step in and deprive Dick of all his contracts and money/power-making opportunities.
Maybe the Rival Corp is a Jr. Executive to their enemy, and sees this as his chance to remove the rank ahead of him so that he can slide up into a more cushy position. Or maybe their would-be savior is higher up, and sees this as a chance to get the ankle-biter from challenging his position in the corporation.
Being a AA corp, they have resources, so they might start with a Decker, tracking the commlink. Find out where it is now, who had it before. Was the commlink purchased with the Runner's real Corp SIN, or with a fake SIN. Are any of his accounts linked to that SIN? Is his current Lifestyle linked to that SIN? It wouldn't be too hard for a Corp to mess with the Runner's money, and potentially hire a hit-team of Runners with the character's own money (unless he keeps it all on Certified sticks). With a proper data trail, maybe they can trace it back to the rest of the group, and find out where the rest hang out, or any safehouses, so that they can arrange ambushes elsewhere.
Since the whole group previously worked for this Corporation, it is not likely that just this particular character will be dealt with, and not the entire group. So ultimate, a faked death will probably be necessary, or working for this other Corp in the company and relying on his protection (and being a slave tot he company again), or going balls out and trying to take this particular Exec out, and hope that with his death, the threat to the group's lives stop.
I once played a Character that was essentially a Corp assassin, that was betrayed by her employer. She joined a group of runners to accomplish something, and her employer bombed their payment, and tried to kill them all. Through a chance situation, the bomb went off while the money was somewhat isolated from the group, so only major injuries occurred, no deaths. My character in particular took a vow that day to kill that particular exec, and hope that the company wouldn't take it amiss.. and if so, she would then go on to take out the company (knowing that she was far outmatched against the entire corporation, but willing to die trying if it came to that).
In any case, it definitely gives the GM plot hooks and game material to last for a while. You can run published material, and break up any slow bits in the middle with anonymous hit teams, leaving the group to wonder if they are related to their current job, or this looming corporate threat. Fun times.