I think it depends on how risk averse you are, if you're willing to press on you may potentially end up with a higher valuation or it could start going wrong and you've got no chance of getting as strong an exit. Also depends on your motivation about building a business, if it's about money then taking a strong early exit is a sensible idea, if it's about building the business and exploring it's future then selling and seeing your vision disappear is probably a worst fate than losing out on the money.

I'd personally sell and I'm not very risk adverse, I always push for more when I'm gambling, but if you're exiting at a $1bn value you're going to have enough to explore most ideas without worrying about outside investment.