We have lived in Europe as well as traveled there many times (also to all the other continents except Antartica).
We have done every kind of touring, bus tours, self driving, using the railroad or a rail tour, ocean and river cruises, and more.
In evaluating how we wish to visit places, we always prefer not to take a tour with a large group. However, cost is a factor as well. Every trip we have taken has been well worth the trip, but some we enjoyed more than others.
Prior to the internet booking hotels in a foreign country required an expensive long distance phone call or writing a letter. Your research was limited to guidebooks or references from friends. Sometimes, we would wing it and make that decision when we arrived at the city. 90% of the time that worked OK, but sometimes it was problem.
With the internet, planning a trip on your own is easy. There are so many places that can help, including these boards. The one thing you miss doing it on your own is that tour guides usually know the lay of the land better and can save you time and you won't miss the big stuff. Still, in many cities, you can still find local tours that work well.
Larger group tours are still a key option, when visiting countries like China, Russia, Egypt or places were the languages are a major issue and doing it yourself can result in touring failure. Also, safety and security is better with a group. We still opted for a smaller group with our China trip (27 people), it was fantastic. Our Russia trip included a river cruise and had three full busses full when we weren't on the river boat. Still, that tour was fantastic and well administered by the tour company.
Cruises are great to visit ports like the Greek Islands that are more difficult to visit otherwise. Also, cruises don't require changing hotels frequently. Cruises to scenic places like Norway, Alaska or Iceland are amazing. When our cruise ship entered and exited Venice, also New Your City, that was a memory to preserve.
I don't see the end of group tours, just a pause. COVID 19 will be a footnote in history in 25 years. Tours will likely be going strong by mid-2021 or 2022.