It is true that much of the drop in death rates will turn out to be the natural result of the fact that people can only die once, and many of the frailest people in our societies succumbed to Covid-19 before they could die of the flu or pneumonia or something else. (Many of those deaths turn out to have been eminently preventable, the result of a shameful neglect of the care-home sector in most countries.) Nevertheless, it is reasonable to suppose that dramatically reducing social contact and promoting constant hand-cleaning and other hygiene measures considerably reduced the spread of other infectious diseases than Covid-19, such as the flu which usually kills between 300,000 and 650,000 people annually. Hence, the restrictions have saved many people from dying from other illnesses as well as from dying from Covid-19.
Economic shutdowns, and even work from home orders will have reduced death rates in other ways, too. As the economist Christopher Ruhm has analysed, mortality tends to fall substantially during economic downturns, especially among the working age population. This is because those made unemployed tend to take better care of their health (diet, smoking, alcohol, sleep, exercise) because they have more time and energy to look after themselves than when they were working full-time. The Covid-19 shutdowns have caused vastly more un(der)employment than any normal economic recession, so it it is reasonable to expect the health gains to be proportionately greater. Moreover, the decline of economic activity due to shutdowns or its shift to tele-working have greatly reduced air pollution and traffic accidents that are also major causes of death.
At this point it is hard to tell just how many lives have been saved as an unintended side-effect of our efforts to prevent deaths from Covid-19. However, it is likely to be significant - in the tens of thousands of lives. It is important not to over focus on deaths from Covid-19 just because it is a new way to die and one that makes us feel especially vulnerable. From a moral perspective deaths from any cause are equally important. If we think it would be wrong to end the shutdown restrictions because there is good reason to believe doing so will lead to a preventable increase in deaths from Covid-19 (and we think Trump was an ass for doing just that), then we should also refuse to end the restrictions if that would lead to a significant increase in deaths from other causes. To do otherwise is to assert that we should expend less effort to prevent some deaths merely because they are not caused by Covid-19. This might be explained by a cognitive bias (what philosopher Nick Bostrom has termed the Status Quo bias) to treat deaths from causes we are used to as a normative baseline rather than as a problem to be solved, but it cannot be justified. There is no right number of deaths we should try to return to.
Another way of putting this point is to think of social distancing as a medical treatment that is currently saving many thousands of lives both by preventing new Covid-19 infections and by reducing other causes of deaths. It would be immoral to withdraw such a dual purpose life-saving treatment merely because the pandemic was over. Doing so would foreseeably and unnecessarily result in the deaths of many many people, killed by our willful neglect.
My point is a simple one. If preventing deaths by Covid-19 is a good thing then it is also a good thing to prevent deaths from other causes. This means that we should not apply a lower standard to the value of saving a life merely because we take deaths from some causes as normal and not worth getting upset about. However, it doesn't mean that we should save any life at any price. There are other things that matter besides bare life (or we would already spend 100% of GDP on health care). And anyway, shutting the entire economy down indefinitely would have its own health impact in the long run. Nevertheless, many of the restrictions that have been introduced, such as working from home whenever possible, wearing a mask in crowded public places, staying 1.5 metres apart, frequently washing/sanitising one's hands, and so on would be relatively cheap to maintain and so we have no excuse not to. In addition, more ambitious legislative action is needed to institutionalise ad hoc arrangements we put together in emergency conditions, such as guaranteeing proper sick-pay for everyone; a basic income to shield people from the toxic effects of bad jobs; and a radical reorganisation of care-homes' hygiene and staffing practises.