Multibets is my latest passion, so I'm glad you started this thread. I will read more attentively through it, when I have more time, but even after a brief scrolling, I can say I like many of the replies, so, I'll be back.
As for the question you ask, just recently I placed a multibet with around 180.00 odds, and when I visited the site 2 days later, I saw that I could cash out 20x of my bet, while 2 games still left. I did cash out because I thought 20x was enough, and the very next game ended not as I predicted, so I was happy about my cashing out.
Being in your place I would definitely cash out $389, because it's a big money for me, but I would never bet $70 with 10.36 in the first place. So, if taking $389 wasn't, for you, something to cheer about, you did the right thing and you shouldn't regret it. Cash out only what you are happy with. Good luck next time.