It depends on your definition of ‘missing it.’ I anticipate there will be some special events that will be in the MK for the entire year so more people can enjoy them.
Also, we don’t have opening dates yet for Tron or Guardians, both which are anticipated to open in 2021.
Until more details are available I think it’s impossible to say but I believe you will be there for some of the 50th Anniversary activities if you go to the MK at any time in 2021. The actual 50th Anniversary date is Oct 1, 2021 so you will miss some of the bigger celebrations.
These are only my thoughts though and others may feel completely different from me.