Assuming what has been posted thus far about the vaccine mandate is accurate (25% of the workforce yet to be vaccinated and facing termination with no severance), Fiserv is about to create about 10K-11K disgruntled employees.
Statistically, out of those ~10K people that are now in a super sour mood, a small number of them are gonna shift into geronimo gonzo vindictive payback mode.
Think about the source code, client lists, confidential info, etc. I don't advocate for any unethical behavior, but my gut tells me this is gonna be nuts.
Like the guy in Jurassic Park said, "Hold on to your butts".