I have to confess to recently feeling a little networked-out after  2 days at a conference, as wonderful as it was, and in spite of the amazing networks I formed there. 

I used this realisation, which hit me as I settled wearily into my train seat for the journey home, to take some time to recharge before I had to do it all over again . . . probably the next day. 
If you’re managing a high extravert, at the very least, ask them how they’re feeling, and listen to their response. 

And on a practical level, you could perhaps encourage them to work from home the next day, or to close the office door for a good chunk of their next day’s work – whatever it takes really to help them to charge anew. 

I’m using my own experience here to make a plea . . . please allow them some time and space to recover after a period of outwardness and sociability. They’ll shine all the better for it afterwards