The convention that I have seen is to put the footnotes on the following page. That's the best you can do when you have that catch-22-style conflict.
Well, Plain TeX tries very hard not to let this happen. Same thing for LaTeX which would have take the whole line on the next page. I saw, in French at least, very few books with references on one page and footnotes on next page.
If you take the whole line onto the next page then footnote 8 would have to go with it, meaning that you lose the depths of two lines from that page, which I suspect is beyond the tolerance of the page set-up. I haven't used it, but \setuptolerance[vertical,verytolerant] might give your pages more room for maneouvre in this regard. It might be ugly though. Alternatively you could delve into TeX and give \topskip some glue, but I wouldn't recommend it in case it breaks something ConTeXtual. Then again, there may be an equivalent of Plain's \raggedbottom in ConTeXt, which would then also be a solution... Duncan dh@capdm.com