So I see this as two issues:
1.) Where is my socialization support network?
When it comes to socialization I, personally, need a lot of support/safety. As an introvert who can play the extrovert I like knowing at least a few (3 is a good number) of the people at an event so I can rotate amongst them and not feel that I am keeping any one of them from enjoying the company of other people there. I often do find a "new person" to converse with and then my support people are "off the hook" for the socialization part (the strangers that I tend to connect with are ones that like to have very long and deep conversations about very geeky things that don't interest too many other people - go figure

) Usually my support people will check in with me every so often - I like this!
2.) How is everyone going to get home safely?
I, personally, am more comfortable if I know the "plan" - who is going to be there, who is driving, who is coming home with me, etc. MrS is always very cognizant of this (after all he has known me for 24 years

). Dude is learning, and (now) will often remember to ask and give me a "heads up" if he is going to change horses/plans mid-stream (he is more spontaneous and tends to make spur of the moment decisions without thinking of how that will affect others - but he is getting better at letting me know when it occurs to him, so I have time to get used to the new plan, as opposed to waiting until the last minute).
It also depends on the event - if we are at a friend's house in town and I want to go home because I have to work in the AM but one or the other or both of them want to stay I don't really have an issue going home alone. I know where they are and can come get them in the morning if no one else brings them home. I would be less comfortable leaving them at an event in the big city unless I knew that they had arranged "safe transport" to a known location (i.e. a sober driver to a friend's house that I know).