The regular season schedule is set in advance at the beginning of the season, so buying a regular season ticket between say the Brooklyn Nets and Miami Heat play in Brooklyn on Jan 15th is a sure deal to see the Heat play.
The only way that a regular season game would be rescheduled is if there is something crazy going on that would affect the fans and players safety (extreme weather), which is very rare. I think there was one game out of like 1,200+ NBA games last season that was moved because the weather was so bad that one team couldn’t make it (flights were grounded when a team was scheduled to fly). I think that game was rescheduled to the next day, and people with tickets to the cancelled game are valid for the rescheduled game.
There are In Season Tournament games that are regular season games you can go see like normal regular season games (these are to see who gets into the extra tournament games). The tournament games are scheduled, but the teams aren’t. And teams that don’t get in will play a couple of extra regular season games to catch up to those. All of that will be done by Dec 9th, so you don’t have to worry about it for January games. The Playoffs are the other one that aren’t scheduled and we don’t know who will be playing (well, the Heat are likely to be in the playoffs), but all those will happen starting in April, and since the playoffs are best of seven, only four of the possible seven games are guaranteed to be played, depending on the outcome of the games.
TLDR: If you can buy a ticket in January between a local team and the Heat, you are guaranteed to see the Heat play that team on the day on the ticket.
Embiid is the biggest flopper this season.