A bath is definitely a must for me, although no bath wouldn't stop me buying a property as long as there was space to retro-fit one.
Last house (Georgian, over three storeys and a complete uninhabitable & unmortgageable wreck when we purchased) had a bathroom on the ground floor in a 1980s annex as well as a teensy bathroom on the first floor that was completely unsuitable for 21st century family life.
As we knew quite early on that our decision to make this our forever home was the wrong one and we'd be selling once the project was complete (three years as we did most of the work ourselves), we wanted to keep our options open regarding the layout.
Therefore, although we opened up the bedsit-y annex into a large third reception room, we retained a shower room - reconfigured the layout of rooms, swapping old 'kitchen' space for new shower room and incorporating old bathroom into living space. This gave the option for teenager/elderly relative suite, or even ground floor master suite if a future buyer so wished.
Upstairs we made the old family bathroom a shower room and took the decision to lose a bedroom in favour of a large bathroom that was en suite to the master, but could easily be reinstated as a family bathroom as we retained access from the upstairs landing.
Only thing we didn't do - as we were already over budget - but would have had we stayed, was to fit another bathroom on the second floor to service the two attic bedrooms.
We sold to a family with three DC and they loved the set up.
I would go as far as to say that most family buyers with young DC expect baths, although we did sell my parents' house in 2012 that had the bath removed and a large walk-in wet room type shower fitted a few years previously. The buyers were a young couple planning to start a family.....