Is 89% open label continuity for a Phase II Alzheimer’s drug good?

Cassava sciences, the company behind the controversial Simufilam Alzheimer's drug, recently reported that 89% of phase II study participants elected to continue taking the drug indefinitely after the study ended. Is this a good result, in the sense of being a strong indicator of efficacy and likely stage III success, for an Alzheimer's drug?

As context, Simufilam is reported to have virtually no side-effects – so study participants may have just figured “might as well.” But 89% still seems like a lot