Well, we rent IPs from Damien as well. We pay annually and we have just renewed them for another year.
The IPs were not SWIP'ed to our org for a few months and they were in use. We used to get occasional abuse reports from Damien and they were handled timely. I guess we have received total 4 or 5 abuse reports in the first 6 months that the IPs were not SWIP'ed. The reports were forwarded to us in a timely manner, i.e: 48 hours. This was a manual process so I understand the delay.
I know renumbering is a pain in the ass but it can be handled well in a 3 weeks time. Renting IPs comes with the risk of them getting revoked for whatever reason so one should always have a backup plan.
I suggest monitoring the IP ranges against black lists and act accordingly without waiting for the actual report to arrive. This is a good and affordable one:
http://www.freeblacklistmonitor.com/
Also, paying someone to code a SMTP connection monitor per VPS or IP is not a bad idea to avoid getting blacklisted. This can be easily done via iptables.