Frankly, that's never happened to me, and if you manage your roster effecively it shouldn't ever happen.

You know which players are prone to long-term injuries by looking at the injury status page. If you have two outfielders who COULD get hurt at any given time, you need to have at least five guys on your 25-man roster who are capable of playing in the outfield, just in case. That limits your choices of bench-players, but that's the price to pay for having an injury-prone roster.

Major league teams don't necessarily call up players the same day someone gets hurt. They'll often take two or three days to evaluate the extent of the injury before calling up a minor-leaguer. Having to wait a day or two in PB seems pretty realistic to me.

Based on the way the game is set up, this would probably require major re-programming, and considering all the other problems facing PB, I doubt it's going to be considered.