I have confirmed that all but the following levels in Havoc are solvable at RR 99:
5, 9, 12
These levels require 100% and depend on having a low RR to give you sufficient time at the start to create a safe path for the crowd. They lack "extra" skills for crowd control at RR 99.
Of the remaining 17 Havoc levels, all but the following you can save 100% at RR 99:
10, 16, 20
(I'm actually not totally sure about 16 yet; the known 100% solution will either leak a few lemmings at RR 99, or you need one more builder than given to save the leaked lemmings.)
I've attached save-100% replays for a few levels of interest. The Havoc 17 solution made use of a steel destruction glitch. Havoc 13 is complicated by the RR 99 making it very difficult to assign builder to a left-going lemming in the crowd of right-going lemmings; careful mouse cursor placement and some luck with timing is needed. Havoc 7 is relatively straightforward, except the placement of the blocker on the right side need to be very precise for you to free it later with a digger from the crowd.