McGarry's early season effectiveness is encouraging, for sure, but he certainly won't be starting.
Mercado has a very low WHIP now, but it is a result of an unsustainably low BABIP.
Allard has been awful in pretty much every respect, WHIP over 2.
Castillo is at least striking batters out.
Strahm is indeed probably the short-term injury option, but that weakens the pen, which is, of course, an easier hole to plug, but maybe not with a lefty.