You can drive with it like that for a long time, but if it's lost any of the grease, or gotten dust, water or tiny bits of gravel inside then you'll be up for a new cv shaft as opposed to just replacing the boot. If the clamp went MIA it's spilled a fair bit of its grease for sure because the boot will pull back a fair amount from where it's normally clamped. Was everything immediately behind it a mess with splattered and globs of grease? For the boot that's torn you will definitely be up for a new shaft. The time involved to replace the boot is the same as just replacing the shaft anyway. If you go off-roading then just replace both shafts regardless so one doesn't fail on you when you need it most.