Most states that conduct Runoff elections require that the runoff voters allowed to vote, must have voted in the original vote that created the runoff condition.
Unless there is no rule like that in MS or the Democrats are planning on massive fraud, this is a potential that would go nowhere.
Such is the case here I am pretty sure.
...or the Democrats are planning on massive fraud
That is what they are known for.
Also the GOPe isn't immune from using fraud to keep one of their own in office.
Also one GOPe pol/operative (McConnel I believe) raised somewhere around $800,000 to defeat McDaniel.