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The major factors will be the death rate and how quickly and far it spreads.
You still need living breathing people to produce, ship, and distribute vaccines.
Again, WORST case, if the fatality rate remains around 50%, that's literally a coin toss as to whether you live or die. We need people to grow and make food to eat, to maintain services like water, sewage, electricity, supply lines, to care for children and the elderly that are healthy. 
Its going to be a juggling act between, handling the pandemic and keeping the day to day "running" even if we're limping.
I wonder how prepared we are. Bird flu is substantially harder to contain than Coronavirus. >

The US has vaccines, but not enough to instantly vaccinate 8 billion + people. 
At the end of the day a plan is plan and that's all it is. A lot can happen that leads to better or worse outcomes than nations have planned for.
Best case: Maybe a 1918 type situation.
Worst case: Societal collapse type event.
Most likely, something in between the two. >

Well, we can produce vaccines for influenza more easily than the wait we had for the coronavirus. Of course the biggest problem is that we have a substantial part of the global population being indoctrinated by nonsensical ideas that vaccines are bad - unfortunately bird flu tends to have a higher mortality rate than coronavirus too.
On the other hand, I doubt it will be societal collapse levels.