At the time we got Roussel, I mentioned that I was concerned that he was might well be a spent force. When he first came on the scene a few years ago, he was willing to go with any one and played a very gritty, balls to the wall style. He got into some terrific fights and was hard to play against. But he took a beating doing this. Last year he didn't seem, in the games I saw, as aggressive and he was more and more picking his spots for fights. His production fell as well. I thought that it looked like he was getting beaten down. Latest injury might well be a result of not just the hit in the game (or whatever it was) but a result of a accumulation of blows to the head.
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Canucks' management historically doesn't discount the likely value of a physical player based on his style of play, age and injury history. Some examples:
-giving Derek Dorsett, an undersized fighter, a four year contract with a 62+% raise (1.633 mill to 2.65 mill.) Dorsett's warrior-like performance made him a fan favourite but the Canucks got a total of only 105 games played for their $10.6 million expenditure on Dorsett's extension.
-trading for over the hill tough guy Brandon Prust who was already 31 years old, had missed considerable amounts of time due to injury in 2 of the preceding four seasons and in those 4 seasons had a high of 18 points
-courting 28 year old big-money and term free agent Milan Lucic who, while he'd remained effective was four years removed from his peak days with the Bruins and who had a lot of physical play behind him. Thankfully he signed his front-end loaded, bonus-laden long-term big money contract with the team that had Connor McDavid instead of choosing to play in his home town.
-Erik Gudbranson, signed to a three year extension in the spring of 2018. Gudbranson wasn't old, but had just finished consecutive seasons in which he missed substantial time due to injury with 30 and 52 games in those two seasons, 64 the season before that with the Panthers and was suffering what could have been a long-term injury at the time he was signed to that extension this past spring.
-Roussel, as you point out, a physical player who was becoming less physical and coming off a season far worse than any he'd had in the NHL. After the disastrous season he just had he was signed as a free agent by the Canucks for a 50% increase in pay over his preceding contract and a term of four years.
The Canucks also historically don't seem to discount value of older players due to the risk of age-related deterioration, though this has worked out somewhat better for them.
-Loui Eriksson, then 31 years old with an injury history coming off his highest production year in four years, signed to the same kind of front-end-loaded, bonus-laden, difficult to move long-term big money contract that Lucic had gotten from Edmonton. The Canucks got lucky in that he hasn't had major injury trouble, but his production has decreased to the extent the contract is laughable.
-Radim Vrbata, signed at the age of 33 (an age at which players are almost always losing scoring ability) for 2 seasons at $5 million per season. This worked out far better than it might have-Vrbata had one good season in Vancouver and physically was still able to do well for one season after leaving the Canucks.
-Ryan Miller, signed for three seasons at the age of 34. This worked out as well as it possibly could have-the Canucks got the player they hoped for and Miller, while no longer able to regularly play over 60 games per season, did as well as one could have hoped in resisting fatigue and injury when ridden like a 25 year old.
-Jay Beagle, a 4th line grinder, about to have his 33rd birthday and signed to a 4 year contract with a 70% pay increase, front-end loaded and bonus-laden to make it nearly buyout proof.
So we have a number of gambles on older players and a number of gambles on physical veterans. The gambles on older players have had mixed results (Miller worked out, Vrbata was fine, Eriksson has been a disaster and Beagle is yet to be determined) but the gambles (or attempted gambles) on physical players have so far uniformly worked out badly with the results of the new contracts of Gudbranson and Roussel still to be determined.