As I see it, Pandora's box is well and truly open
It could well be the case. Especially if the disease has already made its way uncontrolled to somewhere like Pakistan (where conditions mean that it is liable to spread quickly and be uncontrolled and the population is more vulnerable) as you state.
The following article is about exactly that possibility, and what happens if China haven't been able to contain the virus at source.
It suggests that it would mean that it could be permanently 'out there' circulating around the globe with “Independent self-sustaining outbreaks [of 2019-nCoV] in major cities globally could become inevitable because of substantial exportation of pre-symptomatic cases”
www.statnews.com/2020/02/04/two-scenarios-if-new-coronavirus-isnt-contained/
Experts envision two scenarios if the new coronavirus isn’t contained
This scenario suggests a 1st wave which would be particularly virulent but the disease wouldn't 'just go away' after that had passed.
It would be a question of doing whatever we could to slow the infection rate to buy time and so we could manage the number of serious cases we had.
This is the point really in terms of how much we worry. Realistically if the virus did come to the UK in an uncontrolled way, self isolation really isn't going to be much of a solution. Simply because you'd also have to avoid every subsequent wave too, because you hadn't got immunity. The only way out of that would be the development of a vaccine. Which isn't likely until 2021 at the very earliest.
I cavat this heavily by saying that the UK might well have lower infection and complication rates anyway for reasons mentioned upthread - before everyone starts panicking - which could give time to develop that crucial vaccine.
As to whether we should worry or not, I'm not for myself and my family - no, the risk is low and if nhs can't cope we can go private.
Well this is a very naive comment. If we do get an epidemic and the NHS really can't cope on a large scale, then nhs v private is unlikely to be relevant at that point. Management of infectious diseases can be deemed as a national emergency and therefore regulated by Public Health England (or equivalent in Scotland, Wales and NI) meaning all health care facilities and medical staff could be brought into state control via the Civil Contigency Act to try and manage the situation. Only 'essential staff' are likely to get priority treatment then.
Not a lot of point in worrying about this ultimately because its a situation beyond the control of the vast majority of us.