That's one of the issues I am trying to adress with
Urbis.
Basically, the rich don't die permanently unless (a) someone goes to a lot of trouble to do something nasty to their very soul, or (b) they die of old age (no one has found a repeatable method of stopping ageing - though lots of people are trying...).
Assassinations still have their use, even if they cease to be permanent in some cases. Sometimes you just want to send a message - dying is a very traumatic experience. Sometimes you want to keep someone from being around at a certain time - after all, it takes some time until you can find the right cleric who can cast it, and he will often need to specifically prepare it, too...
And it's entirely possible to ruin someone by killing him - repeatedly, if neccessary. A
raise dead costs 5,000 gp in materials (according to the 3.5 rules). If you hide the body for long enough, or destroy it throughly, the dead person's relatives have to pay a whooping 25,000 gp for the material components - plus whatever else the cleric in question demands (hey, it's a seller's market at these spell levels...

).
But ultimately, if you want to destroy a man, it is usually wise to ruin him first - financially, politically, and social. And of this are urban adventures made...
Two more points:
- Sometimes, one of the more mercenary churches is willing to case
raise dead for poor people. But this will usually involve some sort of generational contract in which the family pledges to serve the church until the debt is paid off...
- The druidic spell
reincarnate avoids the old age dilemma, as it actually creates a new body for the dead person. Unfortunately, most druids in Urbis absolutely hate the modern city-based civilization of Urbis for a number of very good reasons. Thus, there is a
secret circle of druids that basically blackmails rich and influental people from the cities to disrupt the cities in exchange for an immortality of sorts...