I am on my last tray of Invisalign. I have some questions about what will happen next.

I liken a refinement to a final touch up; you are almost there, but not quite. Since a refinement, unlike a mid-course correction, is usually minor adjustments, the attachments can be left in place and are captured in the new impression sent to Invisalign. I prefer to remove the attachments so that I have the option of replacing them with more effective attachments for the corrections if needed. Whether the attachments are removed or left in place are at the discretion of the provider. The new trays should arrive in about a week depending on where you live, maybe sooner, maybe a little later. Finally, you definitely should wear the last tray until the new aligners arrive. They are acting as retainers to prevent relapse or the tendency of the teeth to return to their former position. Best wishes with you new smile!

It depends on the situation. Generally speaking, attachments can be kept as is while new trays are being made or they can be removed and new ones placed when the new trays arrive. It depends on the type of tooth movements that need to be accomplished by your doctor. Typically it can take several weeks for the new trays to be made as the doctor has to communicate with the technician to instruct them what kind of tooth movements need to take place. Usually a doctor will recommend you to continue to wear the last tray you are on while waiting. However, this is up to your treating doctor and best addressed by communicating with him/her.