I'm always a little worried about Osuna breaking down but it's not unusual for him to have these fluctuations in velocity. His fastball chart shows that he's hit these kind of lows and even worse before. It would be nice however to see a spike fairly soon or this is going to get worrisome. Giving how poorly everything is going anyways, the team would want to be prudent. Shutting him down would feel a lot like punting the season but this might be one that you write off as a lost season in the first place. It's ridiculously early to be so pessimistic about both him and the season but everything looks and feels pretty bleak atm.
http://www.fangraphs.com/pitchfxo.aspx?playerid=13764&position=P&pitch=FA