I made a post here a couple minutes ago here where I talked about the Loner trait and added the fun fact from The Sims Wiki that said

Loners with the insane trait will never need to socialize with other Sims. This is due to the fact that not only will the social need decrease slower because of the loner trait’s effect, but also having the insane trait allows them to use the “Talk to Self” interaction to raise their social need in addition to their fun need.

(TL:DR) That makes me wonder. Could you survive if it was just you, a single Sim, on the map?

It would be a bit of a apocalypse situation. You wouldn't have any rabbit hole locations; though I don't know if having any is a requirement for creating a world. I don't know how it would effect the "Chat with someone" interaction when using a PC or if you could potentially be able to acquire additional Sims through flirting with maids and fire fighters.

It would limit how far you can progress with certain skills and their challenges I image considering you wouldn't have access to seeds for Gardening or other people for the chess challenges for Logic.

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If someone has tried it and uploaded the processes to Youtube I would love to see it. I would be very interested to see how this effects game play mechanics and if you could potentially build up a town in this manner.

If not I may attempt to give it a a go some weekend.

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Edit: I'm giving it a go. Originally I just wanted to kill everyone and see what happens (also to add to the apocalyptic vibe). It turns out even opting out of story progression doesn't stop Sims from moving in to take their spot. I also noticed Sims would continue to show up to social spaces like parks.

I think the next step is to delete every lot on the map.

I've kept my Sim locked in a house in the meantime. Having the loner, insane, and hates the outdoors traits has kept him from never needing to leave the house. The loner and insane trait has kept them from talking to anyone even when using a computer.

I chose the unstable trait as my forth for fun but it seems like they can undergo episodes which change their traits. That could potentially be a major set back.

The Sims 3's Loner trait gives you the Too Many People and the Enjoying Solitude moodlets depending on your situation but your Sims still require social interaction. I feel like a social battery system that depletes as you interact with others be an interesting challenge.

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Fun Fact from The Sims Wiki

Loners with the insane trait will never need to socialize with other Sims. This is due to the fact that not only will the social need decrease slower because of the loner trait's effect, but also having the insane trait allows them to use the "Talk to Self" interaction to raise their social need in addition to their fun need.

Kyle Kyleson married the love of his life, Kyra. They went on to have two children, Arya and Alec. One day Kyle was feeling really jovial and was on a roll with the jokes. He became hysterical and naturally died of laughter.

Everyone was devastated, especially Kyra. She grieved and grieved (longer due to mods) and when his ghost finally showed she was so ecstatic and flirty that they did the do.

Days go by and she’s laughing it up with friends. So much so that she becomes hysterical and you guessed it, died by laughter.

Here lies the problem. Arya is a teen and is taking care of Alec (child). They’re trying to move past the trauma of not only watching one parent die but the other not to long after.

Things are going better for the two when I get a notification that Kyra Kyleson has given birth to a baby boy.

I’m sorry what now?! The baby shows up on Arya and Alec’s friends list and everything, but I have no idea where he is or lives.

Can anyone help me find this list sibling so he can grow up with his brother and sister?

TLDR: Wife WooHoo’d with ghost husband and died while pregnant. Baby was born and materialized when invited over to siblings’ home. How do I move baby in?