So yes lottery rewards can actually get expired, the duration depends on the lottery and the location where you bought it from, power ball time frame is different from mega millions and so on.
I think the best manner of approach is to always check the claiming deadline for a specific lottery to figure out when the ticket will expire, I've not particulate in any lottery before but I am sure that lottery tickets carry their expiring date at the back of the tickets, but not always.
I don't know what country you from, and let me also say that I am not from the US, but I've heard this story about a lucky guy from another country, who won the US lottery, the US government announced him the winner through the lottery website and asked him to come forward and claim his winning, it took about six months before the winner decided to send his uncle to US to go and claim the money on his behalf, with reasons like he doest want his identity known, the winner had to send his uncle who had no issues with being shown on TV and appeasing on newspaper headlines.
So, yeah, when it comes to national lottery at most, as much as every ticket does have expiry dates, there is always an ample space of time given to winners to claim their winnings, most especially, when it involves winning the jackpot.