A remainderman has no right to possession until after the life estate terminates. Hensley v. Conway, 29 S.W.2d 416 (1930). And, a life tenant cannot "abandon" the estate, so as to nullify the life tenant's interest. Coleman v. Banks, 349 S.W.2d 737 (1961).
However, under TX Property Code 5.009, a life tenant has a fiduciary duty to the remainderman, and so if he/she abandons the property and causes waste by doing so, the life tenant can be held liable for all damages
The court can make orders to permit the remainderman to protect his/her property interests. But, without a court order, the remainderman cannot simply seize the property for his own purposes, without risking suit by the life tenant for trespass.
There is one exception to the above. A remainderman could seize the property and take possession, if he/she knows that the life tenant will not return, and ultimately take title by adverse possession as a result. This could, however require up to 10 years of continuous and exclusive possession. So, if there is some chance that this sort of continuity cannot be achieved, then the only recourse would be to file suit for breach of fiduciary and obtain court orders to protect the property.
Hope this helps.