Alec Burleson
Alec Burleson is the most likely player to replace Paul Goldschmidt in 2025. He's played there frequently since being promoted to the majors, and his bat will play at first base. He's appeared in 38 games out of 275 in his career at first base while also seeing time in right field and as a designated hitter.
2024 was Burleson's breakout year of sorts. He started off as one of the team's best hitters through the month of July. His .288/.321/.494 slash line in the first half of the year also included 17 home runs, 53 runs batted in, and a 125 wRC+. He dropped off precipitously in the months of September and October, and he finished those months without a single home run and with an OPS of .510.
Burly is also quite split-heavy. He had a .805 OPS all year against right-handed pitchers, but his .514 OPS against left-handed pitchers made him a platoon candidate by the end of the year. Other lefties on the roster like Lars Nootbaar, Brendan Donovan, Nolan Gorman, Michael Siani, and Victor Scott II make it challenging to justify playing Burleson every day.
Defensively, Burly was a positive defender at first according to outs above average (one), defensive runs saved (two), and UZR/150 (12.6). While he may not be Paul Goldschmidt good, he's at least a plus defender at first base.
However, he would still make for a wonderful platoon candidate at first base with the next player on this list. Considering the bulk of pitchers in baseball are right-handed, Alec Burleson could still see 400+ plate appearances next year even in a platoon role.