Does methyl lithium act as a base in aqueous solution?
Well, you're right, but
Any solvent system moderates (or magnifies) the strength of the acids or bases it solvates. In water, the strongest base is
Such a reaction would be rapid and very exothermic AND QUANTITATIVE...the solution would be stoichiometric in lithium hydroxide. Most of the time, when we store and use lithium reagents, we go to elaborate lengths (i.e. inert atmospheres, flame dried glassware, anhydrous solvent) in order to prevent such reactions.
I could conceive that we could take an anion (methyl lithium itself, or THE ANION formed by reaction with methyl lithium), and treat this with heavy water, i.e.