Firstly, I do not think that every maximal boundary has a smoothing. For example, if the linear system $|-K_X|$ as fixed part, then very likely it contains no smooth element.

On your question of the converse part, we can no expect to find a maximal boundary. For the easiest example, just consider $X=E\times \mathbb{P}^1$, where $E$ is an elliptic curve. Then every element in the linear system of $-K_X$ Is just two copies of $E$, which are smooth. So there is mo nodal boundary.

Firstly, I do not think that every maximal boundary has a smoothing. For example, if the linear system $|-K_X|$ as fixed part, then very likely it contains no smooth element.

On your question of the converse part, we can not expect to find a maximal boundary. For the easiest example, just consider $X=E\times \mathbb{P}^1$, where $E$ is an elliptic curve. Then every element in the linear system of $-K_X$ Is just two copies of $E$, which is smooth. So there is mo nodal boundary.