One potentially huge issue with the don't-go-on-the-road-scenario is that know one knows how all the breaks from facing live pitching would affect Papi's hitting. I'm not aware of any precedent for a hitter doing it over a season, so maybe it does not affect him, but it very well might.
This year, the Sox opened on the road for 7 days. (I'm including off days that are at the start, in the middle of or end of a road trip, because those are days he would not face live pitching.) After that, the trips are 4, 7,4, 7, 8, 7, 7 (this is 4 for the ASB then 3 in NY), 12, 11, 11, 11(including last 3 in NY). Even if the long trips are more evenly distributed throughout the season, there are some big gaps. Is it going to take him 1,2,3... days to get his swing back after an 11-day layoff? Under this plan, you might not get the Papi you expect, even if age does not catch up with him (not that you could ever know if it was the off days, age or both or other factors).