I didn't think this was a thing. My Sim had become good friends with Caleb Vatore, and was invited over one night. After having chatted for a moment, I got a pop-up message stating that he offered her the gift of eternal life - I was baffled and had her accept since it was kind of touching that he thought her worth it. Who would have thought? 
After seeing this, I had to try it out for myself! I adore Caleb, I love him as much as my own Sim and they are currently good friends and boyfriend and girlfriend. I thought it was sweet that he asked so of course she had to say yes!
After a week of gameplay (Game time), she finally got the call, was invited over and offered eternal life!
A funny thing happened though, Lilith decided that it was a great time to jump into the conversation while her brother was in the middle of turning my Sim. Needless to say the interaction failed, as my Sim didn't drink from Caleb, had no uncomfortable moodlet and could ask to be turned. I didn't know that could happen, I love Lilith, but not when she does that, I think she got a little overexcited, lol. (She was really happy when Caleb was turning my Sim, it was kind of cute).
Anyway, I wound up going back to an earlier save so Caleb could try again and it worked this time.
I'm wondering if that's a bug though? I mean, I know interference from other Sims can cancel some socials but that surprised me!
