I think finding the right balance between giving players the option to make contingency plans and the freedom for that to be taken away is a tough line. I think right now in MMORPG space most games are at the extreme (too easy to escape vs too hard to leave a battle).
I think the main thing we need is for the ability to survey the battlefield and compute our chances of success before engaging in a battle. If its a battle I cant hope to win- then yes I believe it might benefit the players to have an exit strategy. However, escape itself should be a fine art- not something so easily done. And escape should really only be an option *before* engagement has been initiated.
One thing I really thinks get in the way of making contingency plans is 'Stealth'. If players can outright hide in plain view, then this disables pvper's ability to properly analyze the battlefield and make tactical decisions. On the other hand, we also can really use some form of stealth to a degree. It opens up a lot of tactical options for players.
I'm still not sure how to classify EVE Online. Sometimes it appears its almost impossible to make a tactical assestment due to Stealth and Warp Scrambling. Once you get scrambled you're locked down and must fight it out. If you decide to make the call and instruct your gang to flee, then chances are some members will be lost. It's a fine line but I'm thinking EVE Online nailed this one better then most.
In World of Warcraft and it's ilk, Stealth is crazy overpowered. You can hit stealth in the middle of a fight and pretty much escape at will. Another problem stealth can present, if I cannot find the pirates that has just been killing my friends then I cannot enforce order. Stealth allows players to pick fights they can win utterly if not balanced quite right. But on the other hand there are games like City of Heroes where players can acquire loads of +perception thus making Stealth nearly useless in high level pvp.
In the end, I still think FPS games and other genres still have probably the best PVP because Stealth is based on "player skill". If I think a stealthed player is near me in Battlefield 2142 for instance, I can shoot them. They are merely hard to see and it works very nice I play a Recon in that title.
What's even more disturbing is games where its too easy to escape an unfavorable encounter. In City of Heroes, it almost felt like you were fighting cowards 95% of the time. I had to design my build intentionally so I could catch any player on foot to finish them off. People will take off as soon as their health starts to get pretty low. I think these are the situations we want to avoid. Make it unfavorable to escape from a fight you've engaged in. There might be a few different approaches that can be applied. In EVE Online, you'll be Warp scrambled at the begining of an encounter making escape impossible. That's effective but boy does it hurt being on the receiving end of that.
Off hand, I must say I drastically prefer EVE Online approach over most any other title. I'd rather die over and over when my "space" is being blockade by warp scrams rather then having to chase cowards around the map. This makes professions viable such as blockade breakers (yep theres ship designed for this), Recons, and suicide pilots.
It's really a fine line designing PVP titles. There is really so many little things to look out for.