Relapses can last a long time: months - a year even. So not being fixed after five days, even with steroids, is not indicative that it won’t ever improve. Steroids don’t improve the extent of recovery anyway: studies have shown that people who don’t have them recover just as much as those that do - the process is just slower. So it’s not the end of the world if they don’t work - nature is still working to repair the damage. You probably already know steroids have risks and side effects, so if a first lot hasn’t worked, I’m guessing they will not just go straight to another lot, but wait to see how things go.
If he has only had two significant episodes - now, and in 2009 - I’m guessing your partner does not qualify for disease modifying drugs (DMDs), as the usual rule is two clinically significant relapses (or more) in any two year period. However, it all depends whether the “minor things in between” were ever reported, and if so, whether the neuro judged them “significant” or not. There are no concrete rules about this - some neuros treat “significant” as meaning “disabling”, so a purely sensory relapse (abnormal sensations, but no disability) may not always count, for the purposes of deciding whether someone ought to be on DMDs.
Whether this latest episode changes anything is something the neuro might discuss anyway, but if not, you could ask.
Steroids are the only treatment I know of, for relapses - otherwise, it’s just a case of trying to manage the symptoms, which could be by some combination of physiotherapy, pain relief, muscle-relaxants etc.
Hope this helps, but please don’t assume five days is last-chance-hotel. If symptoms hadn’t improved in a year, I’d say chances are they’re around for good, but it’s much too early yet, to be drawing that conclusion.