I don't know anything about D2L except that it sounded a lot like BlackBoard. So in a more generic sense, the questions I would be asking would be along the lines of:
- Is the LMS being used going to be within our future budgets?
- What is their fee/charge model? How does that compare with other, similar tools?
- Will changes we need for future development require an additional charge?
- What additional cost to customize existing tools if required?
- What actual fees do we pay?
- Is there a support contract we are paying for?
- Who owns the data?
- Does the LMS' supplier use our school data for their own purposes? e.g On-selling data?
- If we go to another LMS can we export courses easily?
- Do we have to budget for upgrading our infrastructure to meet the needs of this LMS?
- Has customer support been sufficient to meet our need?
- Has the LMS supplier been responsive to a changing demand as we try to meet changing student need?
- Do we get regular updates offering new learning or improved tools? What kind of cost?
- Is there a clear upgrade and development path?
- Can we build learning plans and future targets around a roadmap for future development of the LMS?
- Do our existing systems integrate with this LMS or can we work towards that integration?
- Has the LMS been adaptable to changes in technology? e.g. cell phones
- What is the current level of frustration of staff for the LMS? Satisfaction survey?
- Can we develop inside this LMS so we can have a set of learning tools to meet our future needs?
Clearly this is not a comprehensive or complete list, but it might spur conversation. I suggest one area to explore is the future; costs, upgrades, development plans, responsiveness to changing external technologies, (e.g.cell phones are getting more an more sophisticated). Also, increasing pressure to adopt less traditional classroom practices is placing demands on any LMS, so how does D2L react to that? Moodle is incredibly flexible here, but is D2L? I don't know but these are some questions that could be asked, or be developed further or be a little less aggressive or more so if needed.
The one advantage Moodle has over everything else is that it can not only be hosted by a Moodle Partner, but it can be self hosted with a high degree of competence by anyone who knows PHP, essentially, and even that is not an absolute requirement. As long as the Network admins are knowledgeable then there is really no reason anyone else needs to get involved at all.
Good luck.