When a goalkeeper goes off on loan, whilst it might be an important step of independence and autonomy, it's imperative that the goalkeeping department still remember that they are principally responsible for the development and improvement of the player, in preparation for their career in the professional game.
As a result, taking an interest in the player and continuing to track their development and situation regularly is imperative, both to the player's sense of unity and commitment to the parent club, and also your ability to intervene, support or empower the goalkeeper as you may need to at any time. There are a number of ways in which this can be achieved:
1) Sending out a scout or goalkeeper coach to watch as many games as possible
2) Maintaining regular contact with the host club's goalkeeper coach or manager
3) Ensuring the goalkeeper is back at the parent club at least once a week
(If the player is on loan at a part-time club, they will likely be in training every day with the parent club)
4) Weekly loan appraisal for the goalkeeper with their parent goalkeeper coach, to discuss any issues, successes and continue to monitor the situation
All of these are working with the idea that, whilst the player understands that they are out of your sight and earshot, they are still very much in your thoughts and all at the club are invested in their success.
The goalkeeper coach has to be aware and proactive in monitoring this situation, not being afraid to pull the plug if the situation has turned sour or it is no longer believed to be in the best interests of the player to remain at the club. Of course, there are a plethora of factors that influence the relationships between clubs that might impact upon the 'politics' of loan deals: as always, it's the job of the goalkeeper coach to protect and advocate for the best by their goalkeepers and the team.