CNS lymphoma relapse. Anyone with experience??

Hello all,

To give you some context, my dad was diagnosed with Primary CNS Lymphoma in the summer of '13 when he was 44 years old. He received high dose chemotherapy and after almost 12 weeks in hospital, he eventually came home. His mobility had deteriorated due to the location of the brain lymphoma as well as having a small stroke. Left sided weakness, chronic nerve pain, amongst other things had rendered him wheelchair confined for the most part. He used his delta frame to get around the house but with great difficulty, and so would often resort to his wheelchair. Fortunately he was in remission for the best part of 5 years, which we are very thankful for. 

Fast forward to 2018 and he was diagnosed with primary vitreoretinal lymphoma (CNS lymphoma in effect) and started a round of chemotherapy injections, six to be precise. However, he only completed three rounds and requested to stop because the pressure was too much for him. A scan in March of this year showed the PVL had spread to the other eye. No treatment was done per dads requests. 

Last month over a few nights dads mobility a lot worse, to the point where family members had to carry him on/off the toilet. We took him in and after a throat biopsy (he was complaining about painless difficulty swallowing) they found lymphoma on the right lymph node. Six weeks after admission and countless scans, a second MRI was done. They decided to do this scan because he couldn't swallow food at this point and almost always choked when he tried to eat. Not to mention his speech became very slurred. The MRI scan showed a relapse in CNS lymphoma and doctors have basically said there is no curative treatment they can offer and it's just a matter of time. Currently he is on steroids to help alleviate the symptoms, and they have made him noticeably perkier. Regarding radiotherapy, as my dad is bed bound and weak in terms of mobility, the toxicity of it outweighs the benefit which is something they want to avoid. This rules out any chemotherapy and clinical trials too. Right now, dad is in the process of being discharged so he can go home where he is more "comfortable". Doctors have given him a matter of weeks to months. The steroids have enabled him to be able to swallow again thankfully but speech is still slurry. It hasn't given him any of his movement back, and he hasn't sat up unaided since admissions six weeks ago. 

I guess my question is, even though I know there is no definite answer, is how long does he really have? How long will the steroids work? What happens once they stop working? I don't want him to suffer. Even as I am asking this, I know no one can really give an answer as the circumstances are different for everyone...  but anything will be helpful