From what youve written I wouldnt necessarily say it was discrimination. With regard to disability, the employer is required to make reasonable adjustments. This wouldnt include promotion to a different job unless the person was capable. It could do, but it doesnt have to.
I'm not 100% clear from your post whether you think the company hasnt followed redundancy procedures, whether the person was passed over for promotion unfairly or whether the company failed to make reasonable adjustments for a disability. It does seem like youre lumping all three things together which may or may not be correct.