TeX does not usually detach footnotes. If they happen to be split off, this is usually due to some formatting problem like a manually specified pagebreak detaching the footnote.
There is one particular case where TeX will move a footnote to the next page: it tries splitting some footnote to get room on the current page. Whether it succeeds or not, the next footnote will float to the next page.
So the "missing footnotes" situation occurs mostly in situations that can't be salvaged using TeX's algorithms anyway, when you have multiple footnotes anchored on one line, and not even the next before last one will fit.
A manually placed linebreak before the floated footnote anchor might be inconspicuous if the paragraph before it is long enough.
The combination of in-paragraph footnotes and the less encumbered page breaking of the bigfoot package will usually defuse a lot of situations for critical editions. But if you have a lot of footnote anchors, picking a few manual linebreaks (or juggling with
\looseness) might still be necessary on a handful of pages per thousand: TeX does not reconsider its linebreaks in the main text based on footnote layouts, and even bigfoot does not meddle in that area.