Oh no... Hoping for the best for McKellen, but I understand the severity of this due to his advanced age.
He truly has always seemed like a genuinely good chap and was pretty open about his sexuality when it was still pretty scary to do so, even though he seems to regret not coming out sooner.
So, here's hoping for, well, whatever good news there can be at this age.
At about half his age and based on my recent recovery speed experience, I predict that if I were to fall off stage now, it would take me two years to have full recovery.
For those concerned and yet to click the link: he's expected to be back on stage by Wednesday and has received scans, so it appears to be no major concern, though of course not quite minor either.