The Lofts at Hayden, if built, will go immediately east of the existing HFL condos- there won't be any empty parcels between HFL, The Lofts and Marina Heights.
3 spots were left unfinished within HFL: the 3rd office tower on the corner of Mill and Rio Salado, a small space intended for a retail annex on the west side of the garage, and a parcel on the south side of the shorter condo building. This last parcel is where the hotel was to be developed, fronting Rio Salado and bringing the height of the combined condotel building up to match the residential-only one to the west.
Here is a rendering for reference:
http://www.owp.com/page.php?q=226
Not sure who owns that parcel and whether they have any intentions of ever bringing in a big name hotel brand to the site. It seems like an upscale hotel on the lake would be a no-brainer given the lack of that kind of quality accommodation in the immediate area, right in the middle of the lake, ASU, Marina Heights, Mill, 202, etc. The Omni hotel will fit the need somewhat, but seems like it's going for more for more of a business/conference market, whereas a lakefront hotel would meet a slightly different niche, IMO.
Regardless, all 3 missing parcels are unfortunately the 3 that would help the most in connecting HFL with Mill and Rio Salado and making it more of an urban and pedestrian-oriented development.