If the July ISP can be used as reference (big if right there), then your COBRA benefit would be 4 mo for 0-10 years of service, 6 mo for 10-20 years, and 12 mo for 20+ years (no I don't know in which block 10 and 20 years falls, this is MBA/HR math). So, 6 months is best estimate.
Second, unless you have a plan in place already, then start looking for something else now while there aren't a lot of other folks in the same situation as you claim you're slated for. Set starting/available date late such that if your manager is wrong then you have a choice at that time. If you can establish an YSA, then max it out. Full amount available without contributions by paycheck deductions. If you can retire (on any of the rules), then there are benefits of doing so if/when the verdict comes down, see circuit for what those are precisely, but in July terms it was worth more than 1K. Also, if you are eligible for sabbatical then take it now (18 = 7 + 7 + 4, so after the new rules you should be eligible for the short form of it now).