An extension with term for Lack wouldn’t necessarily block Nedeljkovic. Correct me if I’m wrong, but I believe the Canes have up to another 5 seasons to play around with before Nedeljkovic becomes eligible for waivers. Not that I think Ned would spend 4 years in Charlotte if he’s as good as advertised, but a realistic path to a starter job at the NHL level could be as follows…
2015-2016 – Flint starter
2016-2017 – Charlotte backup/starter
2017-2018 – Charlotte starter
2018-2019 – Charlotte starter
2019-2020 – Carolina backup
2020-2021 – Carolina starter
If Lack shows that he's the real deal in the early season and if he's willing to sign extension within reason, go for it.
It appears to me Nedeljkovic has 4 years left of waiver exemption, through 2019, unless he plays 11 or more NHL games (regular season + playoffs) in 2015-16 which would shorten it by one season.
While it's possible, it would be surprising if he were ready to be an NHL starter in the next 3 seasons and it would probably be more. Going through this past season's save % leaders, with age becoming a clear #1, with age first starting close to 1/2 the games in brackets if different:
Price 23 (20)
Dubnyk 28 (started 31 to 42 games from age 24-27)
Talbot not yet through age 27 (26)
Schneider 26
Crawford 26
C Anderson 28
Holtby 24 (23)
Rinne 26
Lundqvist 23
Rask 25 (22)
and a few selected others who have had success
Luongo 21
Fleury 21
Hiller 26
Quick 23
Mason 20
Elliott 24 (23)
Pavelec 23 (22)
Bishop 27
Miller 25
Nedeljkovic is 19. As can be seen, it is unusual even for the really good goalies to become a clear NHL starter before 23, though it happens occasionally.