If I wear Invisalign wouldn't my palate bone go back to being narrow and Invisalign might not be effective?

Often the expanded arches are held in place long enough for the bone to remodel and stay.  Invisalign is ok for expansion, but only for minor expansion.  There are better appliances that can be used first, as it sounds like you have done.

It is likely that the arch form will be held in place during the entire treatment, so when all is done it should all stay put.

Since Invisalign can apply enough pressure to move teeth, the aligners should hold your expansion. In fact, a certain amount of expansion is possible with Invisalign, but to a certain degree. Thus, you should not have anything to worry about. Your orthodonist needed the space to make your aligners work more predictably, and your aligners will hold your result.

What you should worry about is more about when your is finished. Expansion as an adult is not stable generally speaking. Thus, wearing your retainers when your are finished are a must. In our practice, patients wear retainers one year full-time, then to bed lifetime to maintain their results.

It sounds like your dentist has the right idea, but the activation seems way too fast.  Palatal expansion can enhance your Invisalign result and can be accomplished  with a removable appliance that pushes against the palatal bone,  is activated slowly (2 X a week), and has good stability.  However the most common type of expansion called Rapid Palatal Expansion (RPE) calls for a more rapid activation (daily),  has been shown to be more unstable.  So since you had a more rapid expansion you may need to hold the expansion longer.  Tthe aligners can be made to hold the expansion you have gained until more stability is achieved.  Wearing retainers at night (and as stability is proven after 2-3 years,  lowered to a night a week) indefinitely after finishing your Invisalign treatment will assure you the best long term result.