Yes, if appropriate academic accommodations were provided, and the student did not meet essential course requirements you may fail the student. You are not required to “water down” or fundamentally alter essential course content or the academic standards by which all students are graded. Laws exist to ensure equal access to education; not to guarantee a particular student’s success or to create an unfair advantage.  As a gesture of student support and a best practice, it is a good idea to periodically remind the class (in a general way) of support services available on campus if you notice that grades are sliding and to document the date and time you did so.