It’s sad, but it looks like they were setting things up for the inevitable back in the crossover when Ollie made some sort of deal with the Monitor. Ten episodes would put the ending near crossover time which usually occurs in episode 8 (although this current season had it in episode 9).
Things could happen a couple of ways. Maybe the show will have the crossover in episode 10 and end with a bang. Perhaps the crossover will be the penultimate episode and there will be a final goodbye episode of Arrow. However, I think the most likely scenario would be to have the crossover occur in its usual episode 8 spot and have a two hour series finale to tie up loose ends and deal with the crossover aftermath.