If someone sends a link to a person's record and that record gets merged there is at least a 50% chance that link is now dead and the user now needs to search for the current merged record.
Sometimes people send links without a name or they send a link to someone who has a name similar to someone else and we want to make sure we are going to that specific person.
If persons 4 and 5 are merged and now exist solely as person 4 then going to the record for /Person/5 should have one of three possible results:
1. Text saying that the /Person/5 has been merged and a link that sends them to /Person/4 - Requires interaction, but does inform them of what's happened in case they were asked if the record should be merged
2. Automatically forward from the page for /Person/5 to /Person/4 with either notice of what's happening or no notice - Very easy for the user in general, but may cause confusion if they get 2 links to compare and they both go to the same page
3. Just load the record for /Person/4 there on the page for person /Person/5. - Even more confusing than option 2 because there would be multiple pages for one person without someone realizing it
I prefer option 1. It makes sure they know the new location of the record and why it happened.