“Medieval” generally refers to about 500CE to about 1500CE (no doubt others will correct me with exact dates and definitions) rather than “that time about 500 years ago”, so I believe that the word “medieval” will continue to refer to that period of time. I’m sure that our current (to us) time period will become known by a different name.

“The 21st century is when everything changes”.

Unless there is a huge disruption in humanity's view on history, yes. The "middle" refers to being the period between classical antiquity and the renaissance.