Colonization will entail a pretty large population of people across all fields of expertise. You will also have all supplies and materials necessary for any sort of contingencies. You're not going to have the electrician trying to improv as a doctor. I think it's highly probable that many people will die, but not in particularly grueling ways, but far more mundane. Around 600 people have gone to space (which I'll define as at least LEO). During this (including training), about 30 people have died. A death ratio of 5% is ridiculously high, and most of the incidents have been far from remarkable. Fire in a capsule, oxygen valve failure, heat shield failure, don't use solid rocket boosters, and so on.

It'll be the same stuff with Mars, except the death ratio will likely be substantially higher. It'll again be from just incidents that will look stupid in hindsight. And they will have been, but when you're working to prevent a billion bad outcomes, a few will always manage to wiggle through the cracks. All things considered I think Mars colonization will probably be far easier than the guys who were engaging in civilization building in the past. Settlers in times past were dealing with hostile natives, hostile waters, unknown diseases, unpredictable weather, even mundane things like rats getting into your rations, and had very little ability to measure or adapt to what they were dealing with. For instance Vasco de Gama (Europe to India guy) took 3 weeks to cross the Indian ocean the first time. On his way back, it took 3 months. By the time he returned, about 70% of his crew was dead.

Colonizing Mars will be absolutely brutal but we will have quite far fewer unknowns. Of course the issues will will have to deal with will be far harsher than anything anybody else ever had to manage, but they are known - and so that really simplifies the process.