Under Tools – Options – Debugging – General, there’s an option to "Show Disassembly If Source Is Not Available.”
Not surprisingly, this is the option you see when you try to step into code when the sources are not available. If this option is unchecked, you’ll get this old favorite dialog:
And of course, if you press Show Disassembly, you’ll get the disassembly.
But let’s say you check the option “Show disassembly Automatically.” This will set the “Show disassembly if source is not available” option back in tools options. And if you want to see this dialog again, meaning you don’t want to always see the disassembly, go to tools options to uncheck it.