Averting Loss of Life and Injury by Expediting SIVs Act of 2021 or the Allies Act of 2021 This bill increases the number of special immigrant visas available to qualified Afghan nationals who worked for the U.S. government or the North Atlantic Treaty Organization (NATO) missions in Afghanistan. The bill also relaxes certain qualifications for such visas. Specifically, this bill makes available an additional 8,000 visas for principal aliens under this special visa program, to be available until all such visas have been issued. (The numerical limitations in this program apply only to the principal alien who applies for the visa, not to any accompanying spouse or child.) Under this bill, an alien may qualify based on a credible basis for concern about the possibility of an ongoing serious threat in Afghanistan due to their work with the U.S. government or a NATO mission, where currently the alien must have experienced such a threat. The bill also eliminates a requirement for each applicant to submit a credible sworn statement describing that threat. Furthermore, for an applicant qualifying for a visa by performing duties for U.S. military personnel stationed with a NATO mission, this bill eliminates a requirement that the duties performed qualify as sensitive and trusted duties. If an alien submits a visa application that included an accompanying spouse or child but the alien passes away before the application is granted, the surviving spouse or child shall remain eligible to receive a visa under that application. Currently, a surviving spouse or child retains eligibility only if the application was approved before the alien passed away.