The economic impact started when the shutdown began and furloughed employees stopped their discretionary spending because they had no idea how long they would have to stretch out that last pay check and life savings.

By the time the effects of the economic downturn are visible (such as airports cancelling flights because they have insufficient traffic control), you can expect that the damage done will take years to unwind.

Just because you get back pay in a month or two doesn't mean you return to the previous level of discretionary spending immediately. You are now a consumer with lack of confidence in the economy. You don't know when the next Presidential tantrum is going to shut down the government.

This will affect all the services that government employees used on a daily basis: cafes, restaurants, laundromats, house cleaning, gardeners, etc.

Consumer confidence may not return till long after this president is ejected, assuming the USA actually has any more presidential elections and the Tumpists don't just take over the country.

> Are people who showed up at work will get paid for those past weeks?

Employees of the federal government will get back pay, at least according to the NYT and others. However, they aren’t currently eligible to collect any sort of unemployment (because they’re technically “working”), and contractors who work with the government aren’t guaranteed back pay.

Even government employees who don't show up for work will get back pay. Hence the high number of no-shows.