Taumalolo's defection forced Kidwell to pick a depleted 24-man squad, scrambling to inform a number of players - including West Tigers back-rower Elijah Taylor and Sydney Roosters front-rower Jared Waerea-Hargreaves - of their selection after earlier telling them their World Cup hopes were dashed.
Adding to the Kiwis' woes are the withdrawal through injury of Melbourne Storm premiership winner Tohu Harris and departing Warriors half Kieran Foran.
Hagan, however, insist the Kiwis will still be a force at the tournament that starts in just over two weeks.
"They're still very strong. They have a nucleus of very strong guys up front. They've got a really good back five that caused us some trouble in Canberra and on the Four Nations trip [in 2016]. The fact that there's no Foran in their group probably hurts them a little bit, but they've got [Kodi] Nikorima and Shaun Johnson of course, so they've got some good talent there that can still get the job done," Hagan said.
"We certainly respect the Kiwis and what they're capable of. They'll be strengthened by the likes of Joseph Tapine and Simon Mannering's had a great year for the Warriors. Danny Levi from the Knights. They've got some good talent and they'll be competitive like they always are."
Hagan wouldn't be surprised to see Tonga at the business end of the tournament.
"They will definitely be thereabouts."