As I understand the rules, you can go rejoin the other side of the battle, but not by using cruise, you have to thrust there. There's no catch 22, just a delay in how fast you get there.
Personally I think cruise should be allowed. Why not? I get bombers and other small craft shield running against my cap ships all the time, thrusting and dodging to 3k out, waiting for shields to come back and the supernova to recharge before doing another run against the cap ship, so the rule doesn't work to stop shield running, except in the very limited situation where the cap ship tries to cruise to shield run itself (and honestly, if you go to fight a cap ship without a train CD that should be your problem and not the cap ships)
But that's not how the rule is. The rules are inconvenient at times to the pvp process, but they should be both understood (this one isn't) and followed equally by all (this one isn't there either).
This is the rule:
5.6 If a player engages cruise engine or docks during a PvP fight, this player is considered fleeing. The fleeing player must leave and may not re-enter the system where the fight took place with any of the characters on his/her account(s) while the enemy (player or players involved in the fight) remains in the system, but no more than 4 hours.
However, the fleeing player can re-engage at will if chased.
Now, if you say "I was no longer in a PvP fight because my engagement with the CG was over and you were 10 k away", then you are also giving every cap ship permission to use cruise to catch up when the battle leaves them, and that's not how it has been on the server. It's fine with me if that's allowed, but it should be clear to everyone what is allowed and what isn't, and everyone should be using the same set of rules rather than some people using cruise to catch up and some people not doing it to honor the rules.