How would transactions take place if miners leave the network?

While I understand the incentives involved in a bitcoin transaction validation; I want to hypothesise a scenario where bitcoin is unattractive to people, and they stop their mining processes.

In this case, how would transactions continue to get processed between bitcoin holders? Can this be a valid scenario to judge the robustness of the network?

One explanation I have is that this is where the cap on number of bitcoins comes into play. Chiefly, transaction fees paid by users will drive validation and “mining” in the traditional sense will stop. The incentives would derive value from the currency; more attractive the currency; better the value for validation.

I have been reading up on the bitcoin architecture recently, and I guess I may have missed some important points. What are some other aspects to this?

EDIT: Thanks to everyone who helped me understand this better.

1. Hashrates (an indicator of computational power reqd. for updating the chain) would also move with demand making the returns on cost less volatile (in event of a price collapse)

2. Highly diversified mining pools make this a “black-swan” event in any case lending increasing credibility to the network.

3. The production cost lends an inherent value to the chain (correctness?) which acts as incentive.

Thanks again!