Miscellaneous topics that do not fit into specific categories.
Hello
To answer your question -
As long as you use the SAME Microsoft account, meaning, the family plan owner will be sending the invitation to the SAME email address you currently use for the personal plan, then no, nothing will be lost.
That said, timing matters. After you cancel your personal plan, your plan will still stay activate til it expires. Set a reminder to do it on the day or the day right after it expires. Don't let it go without any plan for weeks to avoid access/data issue if you have used more than the free storage allowance (5GB for OneDrive and 15GB for mailbox).