The clones can regenerate

Trunks gripped the Brave Sword tightly, his muscles rippling with all the power he could muster. This was a perfect opportunity, one that was so rare it only came around once, and he desperately hoped he could make the best of it. As Cell's body hurtled toward him, he swung straight and true, sunlight reflecting off the tip of his blade. TTCHIING! It sliced cleanly through Cell's body just below the hip, leaving a jagged blue line of light refracting through the air.

Both warriors immediately tensed, expecting the afterimage to fade and Cell to appear close by...but it was no afterimage. A gush of purple blood ran down both his legs and he dropped like a stone.

...

The bio-android pushed his torso off the ground, rolling to one side in the hopes of buying time to regenerate, but Vegeta was faster. His punch caught the monster full in the face, stunning him for a moment; with a twisted grin, Vegeta turned to Cell's severed legs and blasted them into oblivion, then sent his enemy flying straight up with a powerful kick. Trunks lifted his sword again as the monster came straight toward him, ready to slice him from top to bottom. But this time, Cell retained his presence of mind just long enough to throw up his barrier.

"NO YOU DON'T!" the panting monster yelled, summoning his blue protective energy shield.

ZZNNKKKK!

The Brave Sword slammed into the purple forcefield with a spray of orange sparks, a screech that set everyone's teeth on edge. Angry, Trunks continued swinging his sword furiously, smashing into the protective shield over and over. The barrier might have been a purely mechanical technique when used by the cyborgs, but now it was being powered by Cell's evil energy...energy that simply had to yield to the Brave Sword's magic.

...

Out of the corner of his eye, Trunks could see his father charging his most powerful attack, and for a moment hope surged in his heart. So far they had done surprisingly well, exacting significant damage and emerging mostly unscathed. How was it even possible? His sword had done the work of slicing through Cell, but it seemed it had also somehow amplified Vegeta's Galic Gun, making it that much more effective against the evil monster. Now, they were poised to deliver a truly devastating attack—he had begun to believe again.

"HIYAAAHH!" With one final swing, Trunks shouted as his blade broke through the barrier.

In that few moments within the protective casing of his barrier, Cell had been able to sprout new limbs, but they were still dripping with greenish-yellow fluid and were not fully formed. Now that he had broken through, Trunks fired a point-blank energy blast at the monster's lower body to distract him, using its momentum to push himself upward and out of the way. Intent on finishing his regeneration, Cell didn't yet give chase, but rather stayed just where he was. When he then heard Vegeta's cry, emerging from the cloud of smoke left by Trunks' attack, he barely even had time to spin around in horror.

"CELL! YOU SHALL NOT DEFEAT THE BRINGER OF DEATH! NOW, TASTE MY FINAL FLASH!"

Vegeta's favorite move had formerly required a lot more time to fully charge, but the prince had honed his technique after the fight with King Cold. Now, he could concentrate his energy and charge it much more quickly...and it was going to pay off here just as it had against android 17.

"OH, SHIT!" Cell's panicked voice rang out as the energy beam bore down upon him. This didn't make any sense. How did that damn sword hurt him? How had Vegeta's comparatively weak energy blasts stunned him?

"NOO!" he shouted, holding up one hand to try and block the Final Flash...but the golden wave didn't even slow down as it engulfed him entirely, slamming into his body with violent force. Gravity could not contain its momentum; rather than curving along with the surface of the Earth, it pierced through the clouds and atmosphere into space. The Final Flash would extend nearly twelve million miles before dissipating halfway between Earth and Mars.

- Bringer of Death Chapter 53

Cell began quietly reflecting on his path to perfection. The decision to use the multi-form technique had been a stroke of genius...but not without significant risk. He had divided himself under cover of one of Trunks's attacks, his real self slipping into the water silently just moments before Vegeta's Final Flash had incinerated his clone.

It had been a bold move. With his power cut in half by the technique, he left himself open to attack if caught. That's why he had been forced to use the Solar Flare at the last second to stop Trunks and Vegeta. Moreover, merely absorbing Number 18's energy wouldn't have been enough to make up for the lost power; he had gambled on the transformation restoring him to full strength as well as adding 18's power to his own.

- Bringer of Death Chapter 54