General internships has been cancelled so far, according to the information of my mentees. This applies to the companies like McKinsey, BCG, Roland Berger, Kearney
However, internships for the most of the companies have been postponed for several months.
According to this situation I would strongly advise you to get in touch with your HR contact from Kearney, Roland Berger and McKinsey and ask them what is a current situation there and when it makes sense for both of you to do the internship. Basically, work with them on the schedule so that you can still squeeze all your three internships in your schedule.
As regard to your second question, internship is normally not getting cancelled. It could be simply postponed for later. But it'll never be replaced with a full-time offer automathically, unless you need to take some further steps to complete couple of more rounds of interviews to get full-time offer.
Hope it helps you