I suspect that, due to the ways that things are developing in this country, any celebrations would be very low-key. In four or five years time expensive and ostentatious festivities would be deeply unpopular in a country which may well still be suffering an economic downturn. The days when malnourished East Enders would line the street to wave Union Jacks and cheer as the monarch drove past are long gone (if they ever really existed in the first place). The royal family are astute enough to realise that spending large sums in a time of austerity is not a way to retain popularity. Unfortunately for them, the second rate politicians that we have might not see it the same way.
As said, the Queen would probably no longer be fit to carry out anything but the most limited duties at the celebrations and without her the question is: Why? Additionally, you would have had another four or five years of the elderly, a group far more likely than the average population to support the monarchy and attend such events, dropping off the perch.