I can only tell you what we did in a similar (but not exactly the same) situation. (I actually posted about it on here at the time, nearly 5 years ago?)
Our GSD had had a high fever, and been put on antibiotics and something to bring down the fever (I think rimadyl... I know she was given rimadyl, just can't recall the sequence of events exactly at this point). She began pacing the house all night, vomiting, and began having seizures.
Vet said we could send her for an expensive MRI ($2,000) to see if it was a brain tumor, try anti-seizure meds (pheno pills) or put her down. We asked what happened (on the non-existent chance we would opt for the MRI) if they found a tumor. What was the treatment? Nothing. GReat! Waste of $2,000. Right?
Old school vet gave us some phenobarb for her and we took her home. She continued to seize for days. Was blind (I have no doubt). Stopped eating (ever though we were hand feeding her at that point, with rotisserie chicken from the deli) and keeping her hydrated with a syringe.
After the weekend, she slowly seemed to be coming out of it. Her balance was off terribly, and she was blind in one eye. But she could sit up and walk a few steps, very unbalanced. (She couldn't even stand to pee before).
By the next day, she had begun eating more, and was up a little more, walking a little more energetically, aware and alert, but still unbalanced and weak. Then we had out of town company arrive. And she began seizing again.
Took her to a different vet. The gave me a cost estimate for their proposed treatment plan (neighborhood of $600 or something) to hospitalize her, run a bunch of tests, IV fluid and nutrition, meds to stop the seizures, etc. To this day it has never been determined if she sustained some sort of traumatic injury to her head, or if she had low thyroid that brought about seizures causing her to hit her head (without us seeing it happen). There was even speculation that she had a deep ear infection (with shepherds, the structure of their ear canal makes it impossible to visually inspect this without a special instrument that requires anesthesia to use it safely), that caused the fever, and the cascade of following symptoms. Once she was stabilized fully, they did perform this and didn't find any infection. By then, it had been over a week since her initial fever/symptoms began, though. So I don't know if they would have seen evidence of an infection that was cleared up and gone, or not.
Anyway, they got the seizures stopped with diazepam, got her hydrated and on the road to recovery with IVs, antibiotics, steroids, etc. We left her at the vet on Friday morning, and brought her back home about 4 days later. Since that time she has taken anti-seizure preventative meds (pheno) and thyroid medication daily.
We have had NO more problems whatsoever. Best $700 (in total between both vets for that series of treatment/events) we ever spent. She's 11 now (birthday this month) and still brings me toys to play with like a puppy. Getting a tiny bit arthritic, but I will NOT give her rimadyl ever again. I strongly suspect that it contributed to her decline in the early stages of her illness.
I do give her glucosamine and chondroitin supplements, and she is happy.
She did go lame on one leg a couple of years ago. Took her in, and they found nothing, chalked it up to arthritis. Then a month or two later (routine exam with blood work) discovered erlichiosis enzymes or whatever. Gave her the appropriate antibiotics for that, and she was back to excellent health in under 36 hours! (If it is the correct diagnosis, it is easy to treat and there are almost immediate results after treatment, if done in time).
Long story short (too late!) It depends on how well you trust the vet, what you can afford, and how much longevity you expect your furry friend to have left with or without treatment. Our GSD was only 6 years old. Half or less of her expected lifespan really. At 11 years old, if it had happened now, I don't know if we would have gone to the same lengths.
Maybe ask for a 2nd opinion at another vet. Is your vet a younger one, used to treating today's pets as family members, or an old school one who views them as yard animals? That makes a difference in what they recommend, seems to me.
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Oh! And during her recovery at the vet, she regained her eyesight. Apparently there can be a temporary vision loss after seizures. She sees fine now, except a bit of cataract in one eye. :/