I dunno

if it breaks, tray pouring off the butter that rises to the top and saving it.

I have made this sauce 1000 times in my career. I am a pro. Yes the cream does help BUT don't attempt to not use it as a stabilizer if you intend on using the sauce for more than 30 mins, I.E.- 4 hour service. Cream is an excellent emulsifier. If it breaks, quickly put some heavy cream (1cup per tall 1/6 pan of broken sauce) in a sauce pan and start the reduction process. Cook it hard but pay attention not to burn it. Once the cream looses its frothiness and becomes more of a spittle texture, cool it down to warm, not hot!! and slowly whisk the broken sauce in. This technique has gotten me out of a jam time and time again but true white butter sauce does not traditionally involve any cream.. This also works the next day after the sauce has been in the cooler all night but it will break 1/2 the time.