I'd actually be curious. Is it the type of thing where a vaccine ends it? Or will it be like the flu where it's always mutating and so the vaccine helps but it's still always out there in some form.

Not an expert, but creating a perennial vaccine depends on the mutation rate and which highly-conserved regions can be targeted.

One of the potential vaccines enrolling trial patients is made of mRNA that codes for the spike protein needed for entry to cells. [0] If that spike protein turns out to be highly-conserved, then the vaccine will have sticking power. If it's not, but there turn out to be evolutionary trade-offs to adapting around it, it could push the virus to become less aggressive.

0. https://clinicaltrials.gov/ct2/show/NCT04283461

Isn't it only if an effective vaccine is created?

For instance, what if it becomes like the flu? Vaccine exists, but flu still does the rounds.

Additionally, with some reinfections happening, what does that mean? Why didn't the people who had covid-19 a first time have immunity?

It is expected to be more stable than influenza. So regional eradication is conceivable in the long term and it's likely to eventually become one of those diseases that is limited to poorer/harder to reach parts of the world. But that is certainly years away. For now we all have zero immunity.

The relapses are a bit of a mystery but it's not uncommon with viruses e.g. various herpes viruses.

The problem with flu isn't tha the vaccine itself isn't effective, it actually protects you from the strains it's designed to just fine, it's just that the influenza virus is unstable and mutates, leading to new versions that you no longer are protected against. So yes, it depends on how stable COVID-19 is as mentioned below.

Aware of this. It does depend on that, and so will the effectiveness of any vaccine.