I think the resurrect want only last for a couple of days after a Sim dies, so you would have to want this lock if that is something you did want to do?
If you resurrect a dead Sim, all previous relationships are lost - but skills earned in their life are in tact.
To resurrect a Sim, you would need the career reward from the Physic career track or a Secret Society member could 'borrow' it from the Secret Society house. The more money you pay the Grim Reaper, the better the Sim but you could choose to make a zombie?
The ghost should not scare a Sim who was a friend at the time of their death but some ghosts can be mischievous. Knowledge Sims enjoy the experience of seeing a ghost - all others are freaked out and if the bladder is full... well you found out what can happen. :)
A loved one can save the Sim from death by pleading with the Grim Reaper. The Grim Reaper checks the scroll and if is was not really the Sim's time, he plays rock paper scissors with the loved one and if the loved one is successful the Sim will not die.
Once playing Nervous Subject, he died on the treadmill (some kind of combustion) and the Grim Reaper came, looked up the scroll and started crying - I don't know if it was because Nervous was his son or whether because it was not his time? Unfortunately, no one was there to save Nervous from death.. :(