I am curious, how many people were in this community? 10? 50? 100? More? What percent of them decided not to make the transition and left?
There’s no question that you will lose some people in any major transition, but when you arrive on the other side you should gain members over time because the experience has improved so much overall. Not to mention mobile which is usually abysmal on these old forum softwares. However, if you have a small, fixed number of users and there is no possibility for adding members to the community, this can be a risky strategy.