The ADA continues to apply, and an employer cannot simply withdraw an accommodation on a whim. You have established a medical need for an accommodation, and your employer must offer an accommodation if a rewasonable one is available.
The EEOC page giving guidelines on COVID says (in section K.1)
The federal EEO laws do not prevent an employer from requiring all employees physically entering the workplace to be vaccinated for COVID-19, subject to the reasonable accommodation provisions of Title VII and the ADA and other EEO considerations discussed below. These principles apply if an employee gets the vaccine in the community or from the employer.
In some circumstances, Title VII and the ADA require an employer to provide reasonable accommodations for employees who, because of a disability or a sincerely held religious belief, practice, or observance, do not get vaccinated for COVID-19, unless providing an accommodation would pose an undue hardship on the operation of the employer’s business.
Section k.6 further says:
An employee with a disability who does not get vaccinated for COVID-19 because of a disability must let the employer know that he or she needs an exemption from the requirement or a change at work, known as a reasonable accommodation. To request an accommodation, an individual does not need to mention the ADA or use the phrase “reasonable accommodation.”
Employers and employees typically engage in a flexible, interactive process to identify workplace accommodation options that do not impose an undue hardship (significant difficulty or expense) on the employer. This process may include determining whether it is necessary to obtain supporting medical documentation about the employee’s disability.
The ADA requires that employers offer an available accommodation if one exists that does not pose an undue hardship, meaning a significant difficulty or expense. See 29 C.F.R. 1630.2(p). Employers are advised to consider all the options before denying an accommodation request.
It is hard to see how having an employee get frequent COVID tests imposes an "undue hardship" on the employer, as it should impose little or no difficulty or expense on the employer. It seems unlikely that an employer who has accepted such testing as a reasonable accommodation would change its position and seek to deny that accommodation. Even if it did, any such employer still has a legal obligation to consider what would constitute a reasonable accommodation, and to inform the employee what it would accept as a reasonable accommodation before undertaking to terminate employment. If the employer insists that a vaccination is absolutely essential and no alternative will be tolerated (highly unlikely, even hospitals are not taking that position) it must offer the employee a chance to comply or to challenge the decision.
Until the employer indicates that the accommodation of regular testing will no longer be accepted, there should be no reason to take significant medical risks to meet an issue that has not in fact arisen.