Rearrangement considerations in feasibility of SN1 in given reactants
The proposed rearrangement would produce a primary carbocation which, relatively lacking in hyperconjugation, is itself unstable.  The proposed rearrangement therefore is not really plausible.
The &quot;instruction&quot; that the highly strained 1-methyl-cyclopropyl cation cannot be formed may be wrong anyway.  This paper reports a substituted cyclopropyl cation as an intermediate in a reaction between a more complex chlorocyclopropane and an alcohol.