Mortality rate for mumps: 1 in 10,000 (WHO)
Mortality rate from vaccination: essentially zero (NIH); around 5 in 7.5 million (NIH): ‘As for vaccines causing death, again so few deaths can plausibly be attributed to vaccines that it is hard to assess the risk statistically.’ (WHO)
Incidence of permanent vaccine damage in the vaccinated population: even generously taking the numbers of those who apply to the vaccine damage programme, rather than the much smaller number approved: 759 claims in the decade to Jan 2017 against a (conservatively low at 90% of children born in a year) of 6.3 million - so 0.00012%.
In the more generous US system which also compensated for non-permanent damage lasting more than six months, around 20,000 claims have been made in the last 30 years; around 6000 were awarded (including to adults from eg tetanus vaccine). The birth rate in the US is around 3.8 million a year. Even taking a very low vaccination rate, the incidence is vanishingly small.
Now of course, the incidence of mumps is pretty low at 1000-2000 cases a year, more than a third of which are in unvaccinated people (pretty significant given they are a much smaller proportion of the general population). But if the individualists hold sway and herd immunity collapses, that figure will grow, a lot (see the graph earlier in the thread on transmission), and the injury rate from mumps is at least on a par with the injury rate from vaccines.