It's understood that the virus itself could be around for quite some time. However, the self-isolation, social distancing, shutdowns, and lockdowns won't last that long.
The purpose of these measures is to identify those affected and to prevent too many people getting COVID-19 simultaneously. For most it will be a mild reaction, and they won't need urgent care, but they are still vectors to spread the virus, which is why we need to limit interactions for 2-4 weeks. If everyone is continuing to mingle it spreads the virus, creating more vectors, which then puts those who are already vulnerable at even more risk, which leads to an overwhelmed healthcare system... as can be seen in Italy.
Once we "flatten the curve" things will start to return to normal. People will still continue to catch the virus, but the idea is to get it to a manageable level so people who need urgent care will be able to get it. This is for the short-term. Treatments and vaccines are in the works as long-term solutions, but they take time.
