Yes, you will get the check. If your SSDI is direct deposited into your bank account you should get it before the end of April. If you get a paper check for the SSDI you may have to wait a bit longer.
@ceejayoz Gave the answer in a comment, but the official statement can be found here on the IRS website.
Q2. Will I receive a Payment if I do not make enough money to normally have to file an income tax return?
A2. Yes. Eligible retirees and recipients of Social Security
retirement, disability (SSDI), survivors benefits, Railroad
Retirement, or veterans benefits, as well as individuals who do not
make enough money to normally have to file a tax return, are also
eligible for the Payment. This includes those who have no income, as
well as those whose income comes entirely from federal benefit
programs, such as supplemental security income (SSI) benefits. No
minimum income is needed for the Payment.