I had prepared a lengthy response, dear friend, but my computer became disconnected yesterday, so I was not able to save it.
Lord have mercy.
However, I will briefly state that not only can the celebration of Western Easter and Pascha occasionally fall on the same day, but also there can be as much as a five week difference with Pascha falling 35 days after Western Easter. This is because the Revised Julian Calendar which the New Calendarists use, celebrates Pascha on the same day as do the Old Calendarists who follow the Julian Calendar, but the Gregorian Calendar uncanonically violates the Ecumenical Councils in its celebration of Easter.
Except for Pascha, it is the movable feast days of the Holy Feasts of our Lord, the Most Holy Theotokos, and our Holy Saints which now vary 13 days between the Revised Julian Calendar used by the New Calendarists, and the Julian Calendar used by the Old Calendarists.
Rather than worry about a what-if-scenario in the distant future, a date which mankind may possibly never see, it is more profitable to undertake an understanding of what brought about the Gregorian Calendar in the first place, and why the Roman Catholic Church has abandoned not only the canons of the Ecumenical Councils, but all our Holy Canons. Indeed, almost immediately after Vatican I of 1870, the future Pope Pius XII and his canon lawyers started revising all the Holy Canons, eliminating some and rewriting others, thus incurring the anathemas of those Holy Canons. This is one of the major reasons why Roman Catholics today have lost the faith altogether and have discarded so many Christian traditions and beliefs.
The best book I have read on the Calendar Issue is written by Fr. Basile Sakkas on The Calendar Question.