Before we sail on

Dan: We're having a party on our yacht tomorrow.

Tim: You're having a party?

Dan: Yeah. We still have a few more days here before we sail on, so we thought why not throw a party? We've made a lot of new friends during our short stay here.

1) Is there anything about the bold-face part you would change or is it perfectly natural as it is?

2) Is 'sail on' correct and natural if the yacht owners have sailed to the place they're at now (Miami) and held a mini vacation there and are now going to another destination that is not home?

3) Would you keep the question mark after "...why not throw a party?"?

Thanks a lot.