From a more practical standpoint, it is unlikely that the original plaintiff will re-sue, more from the lack evidence to support his case than anything else.
If he does re-sue, it is likely that he has definitive evidence to establish his case and could easily argue that his initial dismissal was because evidence he though was available at the time turned out not to be.
Then I would argue that he should not have wasted the court's time with that lawsuit.
And then add the following (if in federal court (diff't in state court)):
"Voluntary dismissal by the plaintiff is available under F. R. Civ. P.
41(a)(1)(A)(i) if it is filed before “the opposing party serves either an answer or a motion
for summary judgment.” F. R. Civ. P. 41(a)(1)(A)(i). This rule has been “strictly
interpreted” by several courts of appeals including our own to “make clear that only an
answer or a summary judgment motion can extinguish a plaintiff's right to dismiss the
complaint without prejudice.” Manze v. State Farm Ins. Co., 817 F.2d 1062, 1066 (3d Cir.
1987) (listing cases)."
The defendant filed an answer thus extinguishing their right to a voluntary dismissal under the rule.
If the strategy is to delay and increase costs, hitting them with a motion to dismiss before filing a general denial answer certainly accomplishes that goal.