At the end of the day, I can't really see him being convicted and thus I think it's fairly unlikely charges are filed. Each side can call 10 different hockey experts that can say "that's not a natural hockey play, he intended to kick" or "he was off-balance and his leg flew up, he didn't intend to kick" and with how fast it all happened, I think it's going to be hard/impossible to prove beyond a reasonable doubt that it was a criminal act.
A civil suit for damages, if Johnson's family chose to pursue that route, is much closer call as that is a preponderance of evidence (although don't know how it is in U.K., the U.S. is a much more litigious culture so it's likely harder to recover there)