Can you still not be in a wheelchair after having multiple sclerosis for years?

Yes. Some people with MS have a more rapid progression of debilitation while others continue to function with less disability. The medications that are available today have helped manage the symptoms and in some cases slow the progression.
If treated. Untreated MS evolves to secondary progressive in 50% at 10 yrs, 90% at 20 yrs, with compromise with walking in many. But aggressive treatment with potent medications, such as Tysabri (natalizumab) or Gilenya can protect against this progression. So, wheelchair needs these days may be few and far between.
Absolutely. Many people don't realize that MS can remain very mild in very many pts indefinitely; & I've noticed a perceptible secular trend with MS since the the 1st DMT Betaseron (interferon beta 1b) aka Betaferon came out in 1994: In my treated MS population overall, I definitely perceive far fewer relapses, reduced progression of disability, & fewer motor, sensory, cerebellar, cognitive or affective long-term complications.