If we have a leaf shutter lens, will we still need a strobe that Does support High Speed Sync like a Profoto B1 ...

How HSS works with focal plane shutters is that the shutter curtains create a slit which travels across the image plane. The longer the shutter speed, the larger the slit. At a certain shutter speed, that slit becomes smaller than the image plane (sensor/film), and a flash burst will therefore only illuminate a part of it. HSS works by syncing timed pulses from the flash to the slit's travel across the sensor so that the entire thing can get some illumination from the flash.

A leaf shutter, however, works by having overlapping leaves iris in and out, so the sensor is uncovered from the center outwards. HSS pulsing, in this case, would do nothing but illuminate the frame from the center outwards, causing a gradient (kind of like vignetting). So, no, a leaf shutter does not work with HSS.

... or even with a normal Alien Bee can now shoot at 1/2000 second shutter speed because it is a leaf shutter lens?

You probably won't be able to reach 1/2000s (most medium format cameras with leaf shutter lenses max out around 1/800s-1/1000s), but they will sync more quickly than focal plane shutters. And if your shutter speed is within this limit, then you don't need HSS with a leaf shutter lens. The speed, however, is limited by the mechanical speed of the leaf shutter's opening and closing. And at certain speeds and aperture settings, the shutter leaves can still cover part of the sensor/film, and may cause your metering to become inaccurate. It all depends on the individual lens/camera combination.