AT most schools that give need based aid, unless the student is in an approved 5 year program, they will only receive 4 -years- 8 semesters of need based aid.
Please clarify, as to why would your student need 6 years to graduate. Are you talking about taking a leave and coming back?
If your kid needs extra time due to academic difficulties (retaking classes) anything over those 8 terms of institutional aid, is on you. At our house kid knew that they were on the 4 year plan, not the 4 year, i have to do summer school, not the I need another year because I changed my major, want to double major, etc.
If your child is chronically ill and may need to leave school, you should definitely look into tuition insurance