Scripture leaves this question open
The Bible does not plainly explain what happens to an individual animal after death, or say that every pet will be in heaven. That uncertainty can be painful, especially when a pet has been a faithful companion. Still, it is better to be honest than to offer certainty God has not given.
The unanswered question does not mean animals are unimportant to God. He made them and sustains them. Psalm 104 describes living creatures looking to God to provide the food they need (Psalm 104:27). Your affection for an animal is not small or foolish in God’s sight.
These wait all upon thee; that thou mayest give them their meat in due season.
God notices and cares for animals
Jesus pointed to sparrows to help people understand the Father’s attentive care. Even birds that seem ordinary or unnoticed are not outside God’s knowledge and concern (Matthew 10:29). This does not settle the question of a pet’s eternal future, but it does show that God is not indifferent to the creature you loved.
The Psalms also speak of God preserving both people and animals (Psalm 36:6). Animals are part of his good creation, not merely objects for human use. God knows their lives more fully than we do, and his compassion is wider than our understanding.
Creation has a promised renewal
Christian hope is not only about leaving the physical world behind. Romans says that creation itself will be set free from its present bondage to decay and share in the freedom connected with God’s children (Romans 8:21). This gives good reason to believe that God’s final purposes include the renewal of the world he made.
Isaiah gives a prophetic picture of God’s peaceful kingdom in which animals live without the violence and danger familiar in the present world (Isaiah 11:6). Christians differ about how this picture will be fulfilled, but it points towards restoration rather than the abandonment of creation.
Because the creature itself also shall be delivered from the bondage of corruption into the glorious liberty of the children of God.
Grieve with hope and trust
Losing a pet can bring real grief. Their presence may have filled a home with comfort, routine, laughter, and companionship. You do not need to minimise that loss. You can tell God that you miss them, thank him for the good gift their life was, and bring your questions to him honestly.
God promises to make all things new (Revelation 21:5). That verse does not specifically promise that every pet will return, so it should not be used to make a guarantee. But it does give a firm basis for trusting the character of the God who made animals, sees them, and will renew his creation.
And he that sat upon the throne said, Behold, I make all things new. And he said unto me, Write: for these words are true and faithful.